EP0419459A1

EP0419459A1 - Gas distributing and infra-red radiating block assembly

Info

Publication number: EP0419459A1
Application number: EP88906429A
Authority: EP
Inventors: Reinhold C. Roth
Original assignee: Devron Hercules Inc
Current assignee: Devron Hercules Inc
Priority date: 1988-06-17
Filing date: 1988-06-17
Publication date: 1991-04-03
Also published as: WO1989012784A1; EP0419459A4; JPH04500997A; CA1336258C

Abstract

L'ensemble brûleur radiant décrit, qui est destiné à un brûleur infrarouge au gaz, comprend un premier bloc (24) de matériau perméable servant au transport et à la distribution d'un mélange d'air et de gaz de combustion. Un second bloc de matériau (25) ayant des propriétés différentes du matériau du premier bloc achève le transport et la distribution du mélange et forme une zone de combustion dans laquelle le mélange brûle et chauffe la surface externe du second bloc jusqu'à la porter à l'incandescence en vue de permettre un rayonnement infrarouge efficace. Les espaces à travers lesquels le gaz s'écoule dans le second bloc (25) sont plus grands que les espaces à travers lesquels le gaz s'écoule dans le premier bloc (24), de sorte que le mélange se dilate pour former un mélange turbulent dans le second bloc. Des espaces d'écoulement de gaz de grandeurs variables peuvent être prévus dans chaque bloc de matériau. Des matériaux céramiques sont utilisés pour résister aux températures élevées.The described radiant burner assembly, which is intended for an infrared gas burner, comprises a first block (24) of permeable material used for transporting and distributing a mixture of air and combustion gases. A second block of material (25) having properties different from the material of the first block completes the transport and distribution of the mixture and forms a combustion zone in which the mixture burns and heats the external surface of the second block until it brings it to incandescence in order to allow efficient infrared radiation. The spaces through which the gas flows in the second block (25) are larger than the spaces through which the gas flows in the first block (24), so that the mixture expands to form a mixture turbulent in the second block. Gas flow spaces of varying sizes can be provided in each block of material. Ceramic materials are used to resist high temperatures.

Description

GAS DISTRIBUTING AND INFRA-RED RADIATING BLOCK ASSEMBLY

FIELD OF THE INVENTION

This invention relates to gas-fired infrared burners and in particular to how the gas is distributed to the combustion zone and allowed to burn so as to efficiently emit radiation energy.

BACKGROUND OF THE INVENTION

In prior art burners, the gas is distributed to the combustion zone through specially designed orifices or parts which are formed within a unitary block or plate of ceramic material. However, it is important to note not only that this does single block/plate of material serves to transport and distribute the gas to the burning zone, but also that the top layer of that same material serves as the combustion zone, which on being heated to incandescence also serves to produce the infrared radiation or radiant heat flux. Thus, it is clear that the unitary material of prior art burner blocks serves at least four functions: namely transportation, distribution, combustion and radiation.

BRIEF SUMMARY OF THE INVENTION

Since these functions require different material requirements in order to operate efficiently, it is an object of this invention to provide different materials and/or materials haviang different properties for these functions and thus, to provide a composite rather than a unitary material for these functions. In a special case, which involves the function of reverberation/enhancement, which in prior art burners is effected by a separate layer of material lying above the main unitary block of material, it is also an object of this invention to combine this separate special layer into the composite block assembly of this invention.

By providing the proper material for these functions, it is a further object of this invention to maximize the performance of these functions so as to increase the radiation efficiency of infrared burners.

Thus, in its broadest aspect, the invention is directed towards a method for providing a burner assembly for gas-fired infrared burners, which comprises:

(a) providing means comprising a first block of material for transporting and distribut ing a mixture of combust ion gas and air;

(b) providing means comprising a second block of material, which has properties different from the material in said first block, for completing said transportation and distribution of said mixture and pro viding a combustion zone, wherein said mixture can burn and heat the top surface of said second block of material to incandescence, such that it will produce very efficient infrared radiation; and

(c) combining said first and second blocks of material to form a burner assembly.

Similarly, the invention is directed to an appaaratus which provides a burner assembly for gas-fired infrared burners, which comprises:

(a) means comprising a first block of material for transporting and distributing a mixture of combustion gas and air;

(b) means comprising second block of material, which has properties different from the material in said first block, for completing said transportation and distribution of the said mixture and providing a combustion zone, wherein said gas can burn and heat the top surface of said second block of material to incandescence such that it will produce very efficient infrared radiation; and

(c) means for combining said first and second blocks of material to form a burner assembly.

In the further embodiment, the invention involves a method for producing infrared radiation, which comprises the steps of: (a) forcing a pressurized mixture of combustion gas and air through a multitude of small first spaces connected together in a first block of material, at a velocity which is greater than the velocity of the flame propagation in the mixture, into a second block of material, which, while containing a multitude of spaces connected together which are larger than those of the first spaces, is combined with said first block to form a composite burner block assembly;

(b) allowing said mixture to expand and form a turbulent mixture in said second block; and

(c) allowing said turbulent mixture to ignite and burn, thereby heating the top surface of said second block to a very high incandescence temperature and causing it to produce very efficient infrared radiation.

In a further embodiment, the invention involves a method for producing infrared radiation, which comprises the steps of:

(a) forcing a pressurized mixture of combustion gas and air through a multitude of small distinct channels in a first block of material, each channel being perpendicular to a radiation surface and consisting of first and second sections, the first section having a cross-sectional area smaller than that of the second section such that the velocity of the mixture through said first section is greater then the velocity of the flame propagation in the mixture, the cross-sectional area of the second section being a varying one commencing with that of the first section and then expanding in bowl- shaped fashion until the second section makes contact with a second block of material, consisting of a multitude of spaces connected together, into which the mixture is forced to flow, and which combined with said first block forms a burner block assembly;

(b) allowing said mixture to expand and form a turbulent mixture in said second section of said first block and in said spaces of said second block; and

(c) allowing said turbulent mixture to ignite and burn in said second block of material, thereby heating the top surface of said second block to a very high incandescence temperature and causing it to produce very eficient infrared radiation.

In a still further embodiment, the invention involves a method for producing infrared radiation, which comprises the steps of:

(a) forcing a pressurized mixture of combustion gas and air through a multitude of first small distinct channels in a first block of material, each channel being perpendicular to a radiation surface and having a cross-sectional area such that the velocity of the mixture through said channel is greater than the velocity of the flame propagation in the mixture and being extended until it meets with a second small channel in a second block of material containing a multitude of said second channels which are in direct alignment with said first small channels, the cross-sectional area of the second channels being a varying one commencing with that of the first section and then expanding in bowl-shaped fashion until the second channel makes contact with the top surface of the second block of material, which combined with said first block forms a burner block assembly;

(b) allowing said mixture to expand and form a turbulent mixture in said second channel of said second block;

(c) allowing said turbulent mixture to ignite and burn in said second block of material, thereby heating the top surface of said second block to a very high incandescence temperature and causing it to produce very efficient infrared radiation.

The above-mentioned first block of material, which is also referred to hereafter as the "distribution block", should have low coefficients of both thermal expansion and thermal conductivity, as well as high temperature resistance. Various ceramic materials can meet such needs, for example, bonded aluminium oxide fibers, lithium aluminum silicate, and materials sold under various trade names. The above-mentioned second block of material, which is referred to hereafter as the "radiation block", should, in addition to having high temperature resistance and a low coefficient of thermal expansion, have a high emissivity and/or the ability to receive a surface oxide deposit or coating which exhibits a high infrared emissivity in the wavelength region of 1.5 to 2.0 microns. Silicon carbide is one such material, and there are various metal oxides coatings, which will meet such needs. Preferably, the radiation block should have a high coefficient of thermal conductivity.

When the first and second blocks are "combined" to form a burner assembly, this may be accomplished in a number of ways, e.g. they may be laminated or held together by a chemical bonding/sealing means, or held together mechanically. The overall thickness of the assembly is typically less than 2.5 cm and the second block is thinner than the first block.

As an optional arrangement in any of the above embodiments, a surface screen may be used to increase the overall radiation of the assembly. In prior art burners, a high temperature metal screen is used which has a relatively high heat capacity and takes time to "cool down"; it also has a relatively low radiant surface area. It is therefore a further object of this invention to provide a reverberation/enhancement screen/layer of material, which will have a very low heat capacity and a high radiant surface area of high emissivity.

Thus, the present invention is also directed to a method for providing a reverberation layer for gas-fired infrared burners, which comprises:

(a) providing a burner block which will perform the functions of transporting, distributing and combusting a mixture of combustion gases and radiate the resulting infrared energy; and providing a reverberation layer of material, consisting of a multitude of small spaces connected together, which has a low heat capacity and a relatively high radiant surfaces area of high emissivity.

In a further embodiment, the above burner block may consist of separate layers of material having different properties as already described above.

In a still further embodiment and in line with the burner assembly concept of this invention, this fifth function of reverberation, when provided in the form of a porous reticulated structure, may be combined with or bonded to the main burner assembly as a special layer of material to form an overall composite assembly of three layers of material. Thus, the first layer would continue to perform the functions of transporting and distributing the gas mixture (and flame arresting), and the second layer would generate by combustion the primary infra-red radiation and finally the third layer would enhance this.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will now be described in further detail having reference to the accompanying drawings, wherein:

Figure 1 illustrates, in cross-section, a type of infrared burner unit in which the present invention, involving a composite burner plate/block assembly, may be used;

Figure 2 illustrates a portion of a cross-sectional view of an embodiment of such a composite block, involving separate blocks for distribution and for radiation;

Figure 3 illustrates a similar cross-section of another embodiment involving separate distribution and radiation blocks, combined in one assembly;

Figure 4 illustrates still another embodiment of such a composite assembly; Figure 5 is a graph showing the relationship between the radiant output and the temperature of the emitter; and

Figure 6 illustrates a cross-section of another embodiment involving separate distribution (transportation), primary radiation (combustion) and reverberation (enchancement) layers of material, combined all in one assembly.

THE PREFERRED EMBODIMENTS

Referring to Figure 1, reference numeral 2 illustrates a type of infrared burner unit in which the present invention, involving a composite burner plate/block assembly 3, may be used. Burner block assembly 3 has a first block of material or distribution block 4, to transport and distribute a mixture of combustion gas and air to a second block of material or radiation blook 5, which is different from the material in distribution blook 4. Radiation block 5 will complete the transportation and distribution of the mixture and provide a combustion zone, wherein the gas can burn and heat the top surface of the second blook of material 5 to incandescence (generally in the range of 1100 - 1400°C) such that it will produce very efficient infrared radiation. The mixture is initially ignited adjacent the upper surface of block 5, e.g. by a conventional piezoelectric igniter or pilot flame (not shown). Means are provided to combine the first and second blocks of material, i.e. distribution block 4 and radiation block 5, to form the burner block assembly 3. Such means to hold blocks 4 and 5 together may include chemical bonding, such as molecular bonding, sealing, gluing, etc. and/or mechanical bonding, such as molecular attraction, clamping, etc. Since chemical bonding will depend on the type of block material used, for purposes of illustration only, a more general type of mechanical bonding will be used, i.e. clip-like clamps 11.

Various embodiments of blook assembly 2 are illustrated in Figures 2, 3 and 4. Block assembly 3 forms a gas-air outlet surface or side of an enclosed plenum chamber 8. The mixture of gas and air enters chamber 6 through tube 7 from a source 8. While source 8 preferably supplies pressurized gas and air sufficient to provide the required mass flow rate, in certain cases, a conventional venturi aspirator may be used. The air and combustion gas mixture supplied from source 8 will support complete combustion without the need of any auxiliary air.

A special metal screen or mesh 8 is provided at a short distance from the top of radiation block 5. Screen 8 is heated to incandescence by the combustion of the gas-air mixture, thereby producing radiant heat in addition to that being produced by radiation block 5.

To further reduce flashback, the inlet side to distribution block 4 is provided with a thin metal screen or membrane 10, containing a large number of small holes or orifices, the size of which is small enough to serve as a flame arrester during low gas-air flow rates. However the screens 8 and 10 may, if desired, be omitted.

The length and width of each block assembly will depend on the use to which the assembly is put; consequently, details involving cross-sectional views only are shown. As mentioned above, the overall thickness of the assembly is generally not greater than 2.5 cm. and the radiation blook is generally thinner than the distribution block.

Referring to Figure 2, which illustrates in greater detail a portion of a cross-sectional view of an emobidment of the blook assembly 3 of Figure 1, reference numeral reference 13 indicates such a portion, consisting of a portion of a first blook of material or distribution block 14, comprising a multitude of small first spaces (not shown) connected together, and a second block of material or radiation block 15, comprising a multitude a second small spaces connected together, which spaces are larger than those of the first spaces in distribution blook 14. The size of the first spaces are such that, on forcing a pressurized mixture of combustion gas and air through the small first spaces in the first or distribution block of material 14, the velocity of flow will be grater than the velocity of the flame propagation in the mixture. The sizes of the second spaces in the second or radiation block of material 15 are such as to allow the mixture to expand and form a turbulent mixture and to ignite and burn, thereby heating the top surface of the radiation block 15 to a very high incandescence temperature and causing it to produce very efficient infrared radiation. The material in each block may have a reticulated structure, involving a precise and uniformly distributed cellular pore structure, which may be expressed in terms of porosity, radiation block 15 having a greater porosity than the distribution block 14. As also mentioned, the thermal conductivity and expansion of the distribution block 14 should be low, e.g. the thermal conductivity should be low enough so as to present a oool surface to the gas plenum, i.e. approx. 150°C, to prevent flash-back. Various porous ceramic materials provide such properties. While the thermal expansion of radiation block 15 should also be low, its thermal conductivity, temperature resistance, and emissivity should be as high as possible, silicon carbinde being one such material, or alternatively, it must be able to accept a surface coating of a high emissivity material, e.g. metal oxide coatings, such as those of cobalt, nickel, chromium, and thorium, as well as metal silicates and sillces carbide. Some of these materials may also be impregnated into the top layer. Optional screens 8 and 10 mentioned in connection with Figure 1 may be provided here to advantage: this could extend the choice of porous materials. Depending on the type of reticulated material chosen, the radiation block could be very much thinner than the distribution block, e.g. 206 mm compared to 10-20 mm for the distribution block, which should be thick enough to provide back pressure for the gas-air mixture to allow uniform combustion across a large number of burner surfaces connected to the same manifold. The pore size of block 14 should also be small enough so as to prevent flashback.

Referring to Figure 3 , which illustrates in greater detail a further embodiment of the block assembly 3 of Figure 1, reference numeral 23 indicates a portion of a cross-sectional view of a block assembly, consisting of a first block of material or distribution block 24, comprising a multitude of small distinct channels 26, each channel being perpendicular to the radiation surface consisting of a first section 27 and a second section 28, the first section having a cross-sectional area smaller than that of a second section 28, such that when a pressurized mixture of combustion gas and air is forced through section 27, the velocity of the mixture through the first section 27 is greater than the velocity of the flame propagation in the mixture. The cross-sectional area of the second section 28 is a varying one commencing with that of the first section and then expanding in bowl- shaped fashion until section 28 makes contact with a second block of material or radiation block 25, consisting of a multitude of spaces connected together, into which the mixture is forced to flow. The sizes of the spaces in the second or radiation block 25 are such as to allow the mixture to expand and form a turbulent mixture and to ignite and burn, thereby heating the top surface of the radiation block 25 to a very high incandescence temperature and causing it to produce very efficient infrared radiation.

The materials and design of the channels for distribution block 24 are well known in the prior art. The thermal conductivity and expansion of distribution block 24 should be low, as provided by various ceramic materials, such as aluminum oxide fibers; lithium alumi nium silicate; and those sold under various trade names , e . g . "Cordiorite" " , "Mullite " " , etc . The des i gn of the channels is disclosed in e.g. U.S. Patent Nos, 3,885,907 and 3,635,644. Details for radiation block 25 are the same as those for radiation block 15 discussed in connection with Figure 2.

It will be noted that since distribution and combustion can take place in section 28 of distribution block 24, an even thinner radiation block 25 can be used in this embodiment than in that shown in Figure 2. It may be noted that radiation block 25 can serve to retard "lift-off" of the flame and thereby allow for a wider range of gas-air flow rates/energy inputs. Whether or not combustion takes place in the expanded section of the distribution block 24 will depend on the flow rate, the thickness and porosity of radiation block 25, as well as the design of that particular section.

Referring to Figure 4, which illustrates in greater detail a still further embodiment of the block assembly 3 of Figure 1, reference numeral 33 indicates a portion of a cross-sectional view of the block assembly, consisting a multitude of first small distinct channels 36 in the distribution block 34, Each channel 36 is perpendicular to the radiation surface and has a cross- sectional area such that when a pressurized mixture of combustion gas and air is forced through distribution block 34, the velocity of the mixture through channels 36 is greater than the velocity of the flame propagation in the mixture, each channel 36 being extended until it meets with at least one second, small channel 37 in a second block of material or radiation block 35, con taining a multitude of second channels 37, which are in direct alignment with the first small channels 36. The cross-sectional area of second channels 37 is a varying one commencing with that of the first channels, and then expanding in bowl-shaped fashion until the second channel 37 makes contact with the top surface of the radiation block 36. The size and shape of channels 37 in the radiation block 35 are such as to allow the mixture to expand and form a turbulent mixture and to ignite and burn, thereby heating the top surface of the radiation block 35 to a very high incandescence temperature, causing it to produce very efficient infrared radiation. The materials and design of the channels for distribution block 34 would be the same as for the first meeting of the channels described in distribution block 24 in connection with Figure 3. The design of the channels for the radiation block 35 is the same as that of those shown in Figure 3. The design of the channels for the radiation block 35 is the same as for the second section of the channels in the distribution block 24 and described in connection with Figure 3, i.e. as disclosed in the aforesaid United States patents. The materials for radiation block 35, however, should be carefully chosen, and as mentioned above, in addition to having high temperature resistance and a low coefficient of thermal expansion, they should have a high emissivity and/or the ability to receive a surface oxide deposit or coating which exhibits a high infrared emissivity in the wavelength region of 1,5 to 2.0 microns, e.g. silicon carbide or various metal oxides coatings, as mentioned above in connection with Figure 2. Preferably, the radiation block should have a high coefficient of thermal conductivity. The thicknesses of the distribution and radiation blocks will depend on the type of material and prior art design for the channels that might be selected.

While Figures 3 and 4 show a gradual expansion of the sections or channels, i.e. sections 28 in Figure 3 and channel 37 in Figure 4, the expansion could also be fairly abrupt at first so as to form a bowl with nearly perpendicular sides, rather than a gradual cone-shaped bowl.

The use of the above optional screen should be given consideration, as it will increase the radiation efficiency of the overall assembly. This arises from the following: while the total emissivity is a function of the temperature and radiating surface area, the radiation surface will reach a point of diminishing returns with higher energy inputs; however, a proper screen mounted above the radiating surface will increaase the radiation output, because the screen captures the flue gases and converts this exhaust energy to radiant energy, and also by trapping this cushion of gases, it provides an extension of the effective radiant surface by reverberation, and the same time prevents ambient air from reaching the emitting surface. Such a screen may be made from a high temperature metal or from a reticulated open ceramic structure, as already mentioned above.

While the above discloses a general embodiment, involving separate materials having different properties for the various functions, the preferred embodiments involve the use of reticulated materials having specific porosities. This prefernce arises from the following:

The three critical parameters for an infrared emitter are: surface area, temperature and emissivity. The emissivity varies with temperature and the nature of the material, so by choosing a material which inherently already has a high emissivity, the fact that it has a recticular/porous structure will further increase its emissivity. Various materials are disclosed above, with porous silicon carbide being an excellent example.

For a given radiating material, the radiant flux/energy will increase in proportion to the total surface area of the radiating body which is seen by the absorbing body. As can be seen by comparing the radiating surface of Figure 4 with those of Figures 2, 3 and 6, the surfaces of the porous body 15 in Figure 2, body 25 in Figure 3, and body 45 in Figure 6 are each substantially greater than that of the upper surface 25 in Figure 4 (surface 35 being a typical surface for a conventional emitter). Thus, while the radiant surface of a conventional emitter is a relatively small fraction of the total surface, the radiant surface of the emitter of the present invention is nearly 1001 of the total surface.

Nevertheless, of the three parameters, temperature can be the most important as the radiant output varies as the fourth power of the absolute temperature of the emitter. However, in practice as one tries to increase the temperature of a given emitter, the output levels off because of the nature of the surface and the method of producing the temperature. This is illustrated in Figure 6, where curve (a) is that for a typical conventional emitter and where by incrasing the temperature from T₀ to T₁, the output remains essentially the same. Factors causing this saturation were touched on in the above and include: insufficient contact area between the flame and the emitting material and conventional emitters depend on flame impingement on the emitter surface for heat transfer; further energy input by increasing gas flow merely results in "flame lift-off". Curve (b) on the hand, is typical for embodiments of Figures 2, 3 and 6, which involve a porous/reticulated structure.

As oan be seen, because the emitter of curve (b) has more surface area and a higher emissivity, its radiant output at temperature T₀ will be greater than that of the conventional emitters of curve (a) at the same temperature T₀. However in addition because of the nature of the emitter, the manner in which the combustion is taking place (and the conversion of energy from convection to radiant) within the emitter, and its greater resistance to "lift-off", the curve does not level off as quickly, but continues to rise, making posible a further increase in the output by an increase in temperature of the emitter (through higher gas flows). This invention, therefore, allows one to take advantage of the benefits of the higher temperatures. Thus, when operating at the recommended temperatures for the emitter of the present invention, its emissivity is in the range of 0.6-0.95.

The above aspects have led the inventor to provide a further embodiment in which reverberation/enhancement is preferably carried out through the use of a highly porous/reticulated layer of material, rather than a conventional metal screen. This was mentioned above. In such a case, while the highly porous reverberation material can be located at a very short distance above the primary porous emitter, it is preferable to combine or bond it to the top surface of the primary emitter. This is illustrated in Figure 6, which is a cross-sectional view of the burner assembly of Figure 1 (without the use of clips), indicated by reference numeral 43, i.e. of the various individual assembly units that might make up the overall burner unit. This assembly consists of a first block of material or distribution block 44, comprising a multitude of small first spaces (not shown) connected together, a second block of material or radiation block 45, comprising a multitude of second small spaces connected together, which spaces are larger than those of the first spaces in the distribution block 44, and a third block/layer or reverberation block 46, comprising a multitude of third small spaces connected together, which spaces are still larger than those of the second block. Details of the first and second blocks are given in reference to that illustrated in Figure 2 above.

While the overall assembly can be physically hold together as illustrated in Figure 1, it preferable that the various layers/blocks be bonded together for reasons that will be given below. A typical example for such an assembly is: the first or distribution block may have a porosity in the range of 60-85 ppi and be made from LAS (lithium alumina silicate) or "Mullite"; the second or primary radiation (combustion) block may have a porosity in the range of 25-50 ppi and be made from LAS or silicon carbide (coated or impregnated with a higher emissivity material); the third or reverberation (enhancement) layer may have a porosity in the range of 5-10 ppi and be made from silicon carbide. Thickness of the layers will depend on various factors, but typical ranges are: first block, 10-20mm; second block 2-6mm; and third block 2-6mm.

The advantages given above for a porous emitter (when used without reverberation), will also apply to the above porous reverberator when it is used with an emitter, and thereby make it a more efficient enhancer than conventional screens. However, another important feature for such a reverberation layer of very high porosity is that it can be made from a high temperature ceramic material such as silicon carbide. This material does not degrade easily at the very high temperatures used for emitters and this raises the following further advantages: it has a long operating life and advantage can be taken of the use of still higher temperatures, which in turn increase the radiant output substantially (see curve (b), Figure 5). In contrast, conventional high temperature screens operating at a temperature of 1150ºC have an operating life of only 2000-3000 hours. Since the above porous layer would properly operate in the range 1100-1400ºC, not only would the radiant output be much higher at this temperature level, but the life of the porous layer would be very much greater than that of a conventional screen operating at the lower safer level. Should attempts be made to operate this conventional screen at the higher temperature levels that this invention can operate at, then its life would drop even substantially lower.

Another important feature of the present invention, lies in the fact that conventional burners use metal parts in various areas, as well as for the reverberation screen, and in addition use dense ceramic for the burner itself; the relatively high heat capacity of these materials has the result that when the burner is turned off, the "cool-down period" is relatively long, e.g. 180-360 seconds. While the use of metal parts to hold the assembly of the present invention together is not forbidden, in its preferred form, the various layer/blocks are bonded together chemically, thereby eliminating the high heat oapacity of these metal parts. As mentioned above, the very low heat capacity of the various porous layers makes the overall heat capacity of the assembly extremely low, with the result that the "cool-down period" can be less than 5-10 secs.

Besides resulting in a very short "cool-down", the highly porous materials can also have a very low heat, conductivity, so by choosing such a material for the distibution block, all surfaces, other than those involved in oombustion and reverberation, remain relatively cool to the touch, compared to prior art assembly surfaces, which are so hot that they can ignite flammable material.

These features of very short "cool-downs" and cool outer surfaces are very important in applications involving such flammable materials as paper and textiles. These are important safety features both from a fire hazard point of view as well as for those persons who have to operate the burners and the associated paper/textile manufacturing equipment.

Although illustrated embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be made by those skilled in the art without departing from the spirit and scope of this invention.

Claims

I CLAIM:

1. A method for providing a burner assembly for gas-fired infrared burners, which comprises:

(a) providing means comprising a first block of material for transporting and distributing a mixture of combustion gas and air;

(b) providing means comprising a second block of material, which has properties which are different from the material in said first blook, for completing said transportation and distribution of said mixture and providing a combustion zone, wherein said mixture can burn and heat the top surface of said second block of material to incandescence such that it will produce very efficient infrared radiation; and

2. An apparatus which provides a burner assembly for gas-fired infrared burners, which, comprises:

(a) means comprising a first block of material for transporting and distributing a mixture of combustion fas and air;

(b) means comprising second block of material, which has properties which are different from the material in said first block for completing sai transportation and distribution of the said mixture and providing a combustion zone, wherein said gas can burn and heat the top surface of said second block of material to incandescence, such that it will produce very efficient infrared radiation; and

3. A method for producing infrared. radiation, which comprises the steps of:

(a) forcing a pressurized mixture of combustion gas and air through a multitude of small first spaces connected together in a first block of material at a velocity which is greater than the velocity of the flame propagation in the mixture, into a second block of material, which, while containing a multitude of spaces connected together which are larger than those of the first spaces, is combined with said first block to form a composite burner block assembly;

(b) allowing said mixture to expand and form a turbulet mixture in said second block;

4. A method for producing infrared radiation, which comprises the steps of:

(a) forcing a prssurized mixture of combustion gas and air through a multitude of small distinct channesl in a first block of material, each channel is perpendicular to the radiation surface and consists of two secitons, the first section having a cross-sectional area smaller than that of the second section such that the velocity of the mixture through said first section is geater than the velocity of the flame propagation in the mixture, the cross-sectional area of the second section being a varying one commencing with that of the first then expanding in bowl-shaped fashion until the section at least substantially makes contact with a second block of material, consisting of a multitude of spaces connected together, into which the mixture is forced to flow, and which combined with said first block forms a burner block assembly;

(b) allowing said mixture to expand and form a turbulent mixture in said second section of said first block and in said spaces of said second block;

(c) allowing said turbulent mixture to ignite and burn in said second block of material thereby heating the top surface of said second block to a very high incandescence temperature causing it to produce very efficient infrared radiation.

5. A method for producing infrared radiation, which comprises steps of:

(a) forcing a prssurized mixture of combustion gas and air through a multitude of first small distinct channels in a first block of material, each channel is perpendicular to the radiaiton surface and has a cross-sectional area such that the velocity of the mixutre through said channel is geater than the velocity of the flame propagation in the mixture and being extended until it meets with a second small channel in a second block of material containing a multitude of said second channels which ar in direct alignment with said first small channels, the cross-sectional area of the second channels being a varying one commencing with that of the first then expanding in bowl-shaped fashion until the second channel makes contact with the top surface of the second block of material, which combined with said first block forms a burner block assembly;

(b) allowing said mixture to expand and form a turbulent mixture in said second section of said second block;

6. A method for providing a burner assembly for gas-fired infrared burners, including a reverberation layer, which comprises:

(a) providing a burner block which will perform the functions of transporting, distributing and combusting a mixture of combustion gases and radiate the resulting infrared energy;

(b) providing a reverberation layer of material, consisting of a mutlitude of small spaces connected together, which has a low heat capacity and a relatively high radiant sufrace area of high emissivity.

7. The methods of claims 3 to 8, wherein said material consisting of a multitude of small spaces, in a material of a reticulated structure.

8. The method of claim 7, wherein the said reticulated structure is a porous one.

9. The method of claims 1 to 8, wherein the various layers are bonded togther.