US20060141412A1

US20060141412A1 - Burner plate and burner assembly

Info

Publication number: US20060141412A1
Application number: US11/254,122
Authority: US
Inventors: James Masten; Scott Schutts; Thomas Tompkins
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2004-12-27
Filing date: 2005-10-17
Publication date: 2006-06-29
Also published as: WO2006071481A1

Abstract

In one aspect, the invention provides a burner plate comprising a self-supporting substrate having perforations extending through the substrate, the substrate comprising ceramic fibers and an inorganic oxide coating comprising inorganic oxide platelets on the substrate. In another aspect, the invention provides a burner assembly which comprises such a burner plate.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No. 11/023,181, filed Dec. 27, 2004, now pending.

BACKGROUND

The present invention relates to burner plates containing ceramic fibers and burner assemblies containing such burner plates.
Ceramic materials are useful for many applications including, for example, those in which resistance to high temperatures is required. However, many ceramic materials have a relatively high thermal mass and/or are thermally shock-sensitive.
Gas burners typically operate at high (e.g., combustion) temperatures, and are therefore constructed of materials capable of withstanding such temperatures. Inorganic materials such as ceramics have been used in such burners, at least in part, because of their resistance to high temperatures and combustion.
In some burner designs (e.g., radiant burner or blue flame burner), combustion of gas occurs within or near to a body of ceramic material. Typically, on lighting such burners, the temperature of the ceramic material rapidly rises to the operating temperature of the burner. Variations in the coefficient of thermal expansion (i.e., CTE) that exist within the body of the ceramic material typically lead to an accumulation of stress within the ceramic material as the temperature rises. If sufficiently large, this stress may cause fracture of the inorganic matrix and a resulting failure of the burner.
Current approaches to gas burner manufacture include the use of ceramic and/or metal burner plates and/or radiators. However, such burners may have deficiencies such as, for example, a high pressure drop or high thermal mass that may cause burner inefficiency, unwanted emissions (e.g., NO_Xemissions), and/or fragility (e.g., mechanical or thermal shock sensitivity). Thus, there is a continuing need for materials that may be used in gas burners.

SUMMARY

In one aspect, the invention provides a burner plate comprising a self-supporting substrate having perforations extending through the substrate, the substrate comprising ceramic fibers and an inorganic oxide coating comprising inorganic oxide platelets selected from the group consisting of vermiculite platelets, mica platelets, talc platelets, and combinations thereof, on the substrate.
In another aspect, the invention provides a burner assembly comprising a housing having a plenum chamber; a gas inlet port connected to the housing; and a burner plate covering the plenum chamber, wherein the burner plate comprises a self-supporting substrate having perforations extending through the substrate, the substrate comprising ceramic fibers and an inorganic oxide coating comprising inorganic oxide platelets selected from the group consisting of vermiculite platelets, mica platelets, talc platelets, and combinations thereof, on the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an exemplary embodiment of a burner plate according to the invention.
FIG. 2 is a cross-sectional schematic view of an exemplary embodiment of a burner assembly according to the invention.
FIG. 3 is a plan view of an exemplary embodiment of a burner plate according to the invention.
FIG. 4 is a plan view of an exemplary embodiment of a burner plate according to the invention.

DETAILED DESCRIPTION

As used herein:
“uncoated substrate” refers to a self-supporting substrate, for example, a green substrate which has been dried, before coated with an inorganic oxide coating;
“drying” refers to removal of greater than 90 percent by weight of the solvents (including water) introduced by the first impregnation dispersion;
“calcining” refers to heating to at least a temperature at which any remaining volatiles (including all organic materials and water) that were present in a dried substrate are removed; and
“firing” refers to heating to at least a temperature at which chemical bonds form between contacting ceramic particles of a calcined substrate, typically resulting in increased strength and density.
FIG. 1 shows an embodiment of a burner plate 100 of the invention comprised of a self-supporting substrate 110 having ports or perforations 120 through the substrate. The substrate has a top surface 126 and a bottom surface 128. In this embodiment, the perforations 120 are made up of holes 122 and slots 124. In this embodiment, the holes 122 and slots 124 are arranged in a pattern 126.
In this embodiment, the pattern 126 is described as holes 122 and slots 124 designed in a pattern that is repeatable and reduces fault lines that can cause the part to fracture easily. Pattern 126 also provides a distinctive and ornamental design.
As exemplified in FIGS. 3 and 4, the pattern may also be in the form of a logo, artwork, number(s), or stiffening supports pattern, that is, an area of the burner plate surface having no perforations in order to strengthen the burner plate. Burner plate 300 comprises of a self-supporting substrate 310 having ports or perforations 320 of holes 322 and slots 324 through the substrate. The substrate has a top surface 326 and a bottom surface 328. As shown, logo 330 is formed on the surface of the burner plate 300 using an absence of perforations. Burner plate 400 of FIG. 4 also has a logo 402 on its surface. Logo 402 is made using perforations 420, in this case, slots 424 and holes 422. As shown in FIGS. 3 and 4, any pattern may be formed by a pattern of perforations themselves, for example, holes or slots, or, the pattern may be formed through the absence of perforations, for example, by masking the pattern, and perforating around the mask.
The burner plate can have a thickness of 0.5 millimeter to 10 millimeters or greater and may be any thickness between 0.5 and 10 millimeters.
Referring to FIG. 2, burner 200 comprises housing 212 having gas inlet port 210. Burner plate 213 according to the present invention contacts housing 212 to form a seal that prevents gas from escaping around burner plate 213. In operation, a premixed gaseous fuel-air mixture 220 is introduced into burner 200 through gas inlet port 210. By adjusting the gas flow rate, combustion may be stabilized inside burner plate 213, which in turn heats up and radiates thermal energy 215. Typically, burner plate 213 should be sufficiently permeable to gaseous fuel-air mixture 220 (e.g., by being sufficiently porous and/or perforated) that it does not develop undesirably high back-pressure during use. By increasing the pressure drop across burner plate 213, it is typically possible to cause combustion to occur (e.g., with a visible blue flame) on the external face of burner plate 213. Burners that operate under such conditions are commonly termed blue-flame burners. The burner plates of the invention can also be used in radiant burner assemblies.
The self supporting substrates of the invention are typically in the form of a fabric, such as woven fabrics, knitted fabrics, and nonwoven mats including paper.
Ceramic fibers used to make the uncoated substrates for the self-supporting substrates of the invention may be continuous or may have a discrete length (e.g., chopped fibers) and may be, for example, in the form of individual fibers (e.g., straight, crimped, or rovings), yarns, or a fabric (e.g., woven, knitted, or nonwoven). Typically, the ceramic fibers are sufficiently refractory to withstand heating to a temperature of 1100° C. for more than 100 hours without significant embrittlement, and/or heating to a temperature of 1400° C. for at least a brief period of time (e.g., 1 minute). The ceramic fibers may contain glassy and/or crystalline phases, and be formed using materials including, for example, metal oxides, metal nitrides, metal carbides, or a combination thereof. For example, the ceramic fibers may primarily or completely comprise ceramic oxide fibers formed from metal oxides including, for example, alumina, alumina-silica, alumina-boria-silica, silica, zirconia, zirconia-silica, titania, titania-silica, rare earth oxides, or a combination thereof.
Typically, the ceramic fibers have diameters in a range of from 1 micrometer to 25 micrometers (e.g., from 5 micrometers to 8 micrometers), although fibers with larger or smaller diameters may also be useful. If chopped, the ceramic fibers typically have an average length in a range of from 3 millimeters to 50 millimeters, although longer or shorter fibers may also be useful. Ceramic fibers of different lengths, diameters, and/or compositions may be blended. Typically, the use of longer fibers (e.g., 5 centimeter (cm) or longer) in a green substrate results in high physical integrity of the green substrate.
Exemplary commercially available ceramic fibers include glass fibers, quartz fibers, non-oxide fibers (e.g., silicon carbide, silicon oxycarbide, silicon titanium oxycarbide), as well as those ceramic oxide fibers marketed by 3M Company (Saint Paul, Minn.) under the trade designation “NEXTEL” (e.g., “NEXTEL 312”, “NEXTEL 440”, “NEXTEL 550”, “NEXTEL 610”, “NEXTEL 650”, and “NEXTEL 720”), by belChem Fiber Materials GmbH (Freiberg, Germany) under the trade designation “BELCO TEX”, and by Hitco Carbon Composites, Inc. (Gardena, Calif.) under the trade designation “REFRASIL”.
Although the fibers used to prepare the uncoated and self-supporting substrates of the invention can be sized or unsized, the fibers are typically available in their as-received condition with a size coating present. Typically, continuous fibers are treated with organic sizing materials during their manufacture to provide lubricity and to protect the fiber strands during handling. It is believed that the sizing tends to reduce breakage of fibers and reduce static electricity during handling and processing steps. When making a nonwoven mat by wet-lay methods, the sizing tends to dissolve away. Sizing also can be removed after fabrication by heating the fabric or mat to high temperatures (i.e., 700° C.).
It is within the scope of the present invention for the uncoated and self-supporting substrates and burner plates of the invention to employ one of several types of fiber, including utilizing fibers of different compositions or those made of other materials, for example, glass fibers. Typically, the uncoated substrate, self-supporting substrate, or burner plate comprises at least about 75 percent by weight (or at least about 90, about 95, or even about 100 percent by weight) ceramic oxide fiber, based on the total fiber weight of the uncoated substrate, self-supporting substrate, or burner plate.
Desirably, the uncoated substrate is comprised of a nonwoven mat. Suitable nonwoven mats can be made by a variety of methods, as is known in the art, for example, by a “wet-lay” method, or by an “air-lay” method. In a wet-lay method, fibers are mixed with a liquid medium (preferably water) and other additives (such as surfactants, dispersants, binders, and anti-flocculants) under high shear conditions. The resulting slurry of fibers is deposited onto a screen, where the liquid medium is drained away to produce a fabric. In an air-lay method, individualized fibers are fed into a web forming machine, which transports the fibers by means of an air stream onto a screen, to produce a nonwoven mat. Such processes are well known in the art of nonwoven mat manufacture.
In a typical wet-lay method, binder material such as thermoplastic fibers (e.g., PVA, fibers) are blended at high shear in water. Ceramic fibers are added to the blender. High shear mixing typically causes at least some fibers to break, resulting in an overall reduction of fiber length. Mixing is carried out for a time sufficient to suspend the fibers in the water. Flocculating agent, such as an aqueous polyacrylamide solution, which is commercially available, for example, under the trade designation “NALCO 7530” from Nalco Chemical Co. of Naperville, Ill., can optionally be added during the mixing step to cause coagulation of the fibers if so desired. This aqueous fiber “slush” is then typically cast onto a screen (e.g., a papermaker) and drained to remove the water. The resultant nonwoven mat is pressed with blotter paper to remove as much water as possible, and then dried in an oven to further remove the water (typically, at about 100° C.). The green nonwoven mat is then ready for further processing to form an uncoated substrate.
In a typical air-lay method, ceramic fibers are mixed with a binder material, particularly thermoplastic fibers, in a fiber feeder, such as that commercially available under the trade designation “CMC EVEN FEED” from Greenville Machine Corp. of Greenville, S.C., to form a feed mat. The feed mat is fed into a rotating brush roll which breaks the feed mat up into individual fibers. The individual fibers can then be transported through a blower to a conventional web forming machine, such as that commercially available under the trade designation “DAN WEB” from Scan Web Co. of Denmark, wherein the fibers are drawn onto a wire screen. While still on a screen, the fabric can be moved through an oven and heated to temperatures ranging from about 120° C. to about 150° C. for about 1 minute to melt the thermoplastic fibers and bond the fibers of the mat together. Optionally, or alternatively, the nonwoven fabric can be compressed and heated by passing through laminating rollers, for example, to melt the thermoplastic fibers. The green nonwoven substrate or mat is then ready for further processing to make an uncoated substrate.
Organic fibers such as those made from rayon, polyester, polyolefin, cellulosics can be used as heat fugitive filler materials to help control permeability and to provide flexibility and handling strength and loft to the green mat.
The inorganic oxide coating comprises inorganic oxide platelets selected from the group consisting of vermiculite platelets, mica platelets, talc platelets, and combinations thereof. The inorganic oxide platelets are typically applied to the substrate by dispersing the inorganic oxide platelets in a liquid medium (typically water), and applying the dispersion onto the substrate.
Vermiculite is a hydrated magnesium aluminosilicate, micaceous mineral found in nature as a multilayer crystal. Vermiculite typically comprises by (dry) weight, on a theoretical oxide basis, about 38-46% SiO₂, about 16-24% MgO, about 11-16% Al₂O₃, about 8-13% Fe₂O₃, and the remainder generally oxides of K, Ca, Ti, Mn, Cr, Na, and Ba. “Exfoliated” vermiculite refers to vermiculite that has been treated, chemically or with heat, to expand and separate the layers of the crystal, yielding high aspect ratio vermiculite platelets. These platelets optionally can be ground up to produce small particulate, typically ranging in size (i.e., length and width) from about 0.3 micrometer to about 100 micrometers, with a mean size of about 20 micrometers. This small particulate is still considered to be in “platelet” form as that term is used herein. The thickness of a platelet typically ranges from about 10 Angstroms to about 4200 Angstroms. The vermiculite can be applied to the uncoated substrate, for example, by dispersing vermiculite platelets in a liquid medium (typically water), and applying (e.g., coating) the dispersion onto the uncoated substrate. Aqueous vermiculite particle dispersions are available, for example, from W. R. Grace of Cambridge, Mass., under the trade designation “MICROLITE 963”. The desired concentration of the dispersion can be adjusted by removing or adding liquid media thereto.
The vermiculite can be applied to the uncoated substrate using conventional techniques such as dip coating, spray coating, and brush coating. Preferably, the vermiculite is “worked into” or uniformly distributed into the uncoated substrate. For example, the vermiculite can typically be forced into the uncoated substrate by pressure (e.g., by using a conventional hand held roller; by hand flexing the coated fabric back and forth; and/or by passing the vermiculite coated uncoated substrate between two opposed rolls positioned, or capable of being positioned, such that the gap between is less than the thickness of the coated uncoated substrate). Optionally, the vermiculite dispersion can be heated to a temperature below the boiling point of the liquid media before it is applied to the uncoated substrate. Further, the coated uncoated substrate can be at an elevated temperature (e.g., a temperature at or above the boiling point of the liquid media in the dispersion) before, and/or while the pressure is being applied.
One method for coating the uncoated substrate is to dip the uncoated substrate into a vermiculite dispersion for at least several seconds, remove the uncoated substrate from the dispersion, allow excess dispersion material to drain off, and then dry the coated uncoated substrate in an oven (e.g., at 90° C. for 2 hours).
In another method, vermiculite can be applied to the uncoated substrate using conventional techniques, and prior to drying, the vermiculate coated uncoated substrate can be run between two opposed rolls positioned, or capable of being positioned, such that the gap therebetween is less than the thickness of the coated uncoated substrate. Preferably, the coated substrate is at an elevated temperature (e.g., a temperature at or above the boiling point of the liquid media in the dispersion) before, and/or while it is passed between the rolls.
In another embodiment according to the present invention, mica platelets are secured to the uncoated substrate. The mica can be secured to the uncoated substrate in a similar manner as the vermiculite platelets discussed above. Examples of useful micas include, but are not limited to, phlogoplic micas, muscovite micas, and combinations thereof. Mica coated papers are commercially available.
In another embodiment according to the present invention, talc platelets are secured to the uncoated substrate. The talc platelets can be secured to the uncoated substrate in a similar manner as the vermiculite platelets discussed above.
After the uncoated substrate is coated with an inorganic oxide coating and dried, the self-supporting substrate can be perforated, that is, holes and/or slits are made in the substrate. The perforations may be made, for example, by laser, die, and/or hydrojet. Such perforation means may be utilized using software, such as that available for Computer Aided Design (CAD). The perforations may comprise less than 60% of the surface area of the burner plate, and in other embodiments, less than 59, 58, 57, 56, 55, 54, 53, 52, 51, 50, 45, or 40, but not less than 10%, and in other embodiments, not less than 9, 8, 7, 6, or 5% of the surface area of the burner plate. The number or pattern of perforations may be tailored to provide the desired efficiency for the application. For example, patterns or logos can be used to adjust the efficiency, change the pressure drop, and/or strengthen the burner plate, without changing the overall size of the burner plate. The perforations can also be made in the green substrate or in the uncoated substrate. Laser perforation provides perforations, for example, holes and slots, that are angled during cutting, that is, have a larger diameter or opening near the top surface of the burner plate and a smaller diameter or opening near the bottom surface. The larger openings help hold the flame closer to the top surface of the burner plate.
In another embodiment, the invention provides a method of making a burner plate comprising the steps of providing an untreated or uncoated substrate comprising ceramic fibers, treating the uncoated substrate with an inorganic oxide, drying the coated substrate, optionally, sintering or firing the coated substrate, and perforating the coated substrate. Perforating the substrate may also be performed on the green substrate or the uncoated substrate.
Optionally, the coated substrate can be coated with a water repelling material. An example of a suitable water repelling material includes dispersions of polytetrafluoroethylene (PTFE) such as those available from Dyneon LLC, Aston, Pa. The water repelling coating may be added to the substrate as part of the inorganic oxide coating, for example, as a dispersion, or after the coated substrate has been formed.
Optionally, the hardness and durability of the burner plate can be increased by use of a “wash-coat” that comprises materials that bind to the fibrous and particulate materials within the burner plate. This wash-coat treatment can be comprised of metal oxide and/or metal non-oxide materials in particulate or sol forms. The wash-coat can be in the form of an aqueous or organic solvent slurry dispersion or as a aqueous or organic solvent-based solution. These wash-coats can be made over a range of viscosities and formulations.
Examples of useful wash-coats include water-based solutions of “ONDEO-NALCO 1050”, “ONDEO-NALCO 1042” or “ONDEO-NALCO 2329” silica (silicon oxide) sols, available from the ONDEO-NALCO Company, Naperville, Ill. By controlling the ratio of water to silica sol, the hardness and coefficient of thermal expansion (CTE) of the resulting wash-coated burner plate can be varied. These silica sols are typically highly loaded (>30% solids) sols. Such sols dry quickly when exposed to temperatures near 100° C. and leave silica particulates that coat the burner plate components and which may fuse to the burner plate components at calcining temperatures.
Other examples of wash-coats are, for example, a mixture of a sol such as, but not limited to, “NALCO 1050” silica sol in with (i) a metal-oxide or metal non-oxide powder, or (ii) a metal-oxide or metal non-oxide precursor sol, or (iii) a metal oxide or metal non-oxide dispersion. Such mixtures can be stirred, blended, or otherwise agitated to provide a solution or homogeneous dispersion.
Examples of metal oxides and metal non-oxides include, but are not limited to, aluminum oxide, zirconium oxide, silicon carbide, silicon oxide, titanium dioxide, and combinations thereof.
Burner plates according to the present invention may be used to support a number of different kinds of catalysts to assist in the reduction of other pollutants (e.g., NO_X) in the exhaust from combustion. One way to catalyze a burner plate according to the present invention is to introduce catalyst precursors, catalytic materials, or a combination thereof at one or more points in the burner plate manufacturing process. Such catalytic components may be introduced in the initial green substrate forming process, in one or more impregnation steps, or a combination thereof.
Exemplary catalytic materials include materials comprising metals such as platinum, palladium, rhodium, iron, nickel, silver, ruthenium, copper, gold, and combinations and alloys of these metals and compounds of these metals and metal oxides such as iron oxide, copper oxide, alkaline earth oxides, and alkaline earth aluminates, rare earth oxides, rare earth aluminates, cerium oxide, vanadium oxide, manganese oxide, cobalt oxide, first row transition metal-rare earth oxide compounds and mixtures, oxides having perovskite and perovskite-related crystal structures, metal phosphates and phosphate-oxide mixtures, and NO_Xreduction catalysts (e.g., rhodium supported on alumina, ceria, or alumina-ceria), and combinations thereof. The catalyst(s) may be present as particles of catalyst material(s) or catalyst material(s) on support particles, where the particles are adsorbed on the surface of the burner plate.
In one embodiment, the catalytic metal or metal compound may be applied to the green substrate as a metal salt solution. The metal salt may then be, for example, chemically altered (e.g., chemically reduced) to the active metal form, or thermally decomposed to the active metal form, and adsorbed onto the burner plate. In another embodiment, the catalytic metal or metal compound may be applied to the burner plate in the form of a colloidal dispersion or adsorbed on a colloidal carrier by dipping or other impregnation techniques. Catalytic metals or metal compounds may also be applied to a burner plate by conventional gas phase deposition techniques.
Additionally, materials can be added to the wash-coat to affect the insulative properties and/or emissitivity of the burner plate. Materials for catalytic activity may also be added to the wash-coat.
In certain burner applications, burner performance can be improved by providing a burner plate having a high burner surface area to geometric burner surface area ratio. Such a ratio can be achieved by using a ceramic fabric having surface protuberances on its surface. The protuberances may be formed during the process of making the ceramic fabric by forming the fabric on a suitable screen having the desired hole and/or slot spacings or on screens that are pleated or dimpled. Alternatively, such protuberances can be formed in the green substrate by using a suitable mold.
Burner plates according to the present invention may have any shape (e.g., a sheet that may be substantially planar or nonplanar, a cone, a cylinder, or a thimble), the choice typically depending on the intended application. Exemplary methods of shaping the self-supporting substrate include, for example, molding, embossing, and cutting the green substrate to a form that is maintained through the various processes described hereinabove to give a shaped burner plate.

EXAMPLES

General Procedure for Making a Ceramic Fiber Burner Plate
An uncoated substrate was prepared according to the “Wet Lay Method II” procedure of U.S. Pat. No. 5,955,177, but without being printed with a metal oxide pattern, the disclosure of which is incorporated herein by reference, having dimensions of 6 in×6 in×0.125 in (15 cm×15 cm×0.32 cm). Aluminum borosilicate fibers (0.5 in (1.2 cm); and 200 g/m²basis weight, obtained under the trade designation “3M NEXTEL 312” from 3M Company) were used.
The uncoated substrate was dip coated in an aqueous vermiculite particle dispersion (available from W. R. Grace of Cambridge, Mass., under the trade designation “MICROLITE 963”) and pressure was applied with a hand held roller, removing the excess dispersion. The wet ceramic substrate was placed on a perforated steel plate in a forced air furnace (obtained from Despatch Industries, Minneapolis, Minn., under the trade designation “DESPATCH V SERIES”) and dried for 30 minutes at 90° C., yielding a coated ceramic substrate with an add-on of 50-60 weight percent “MICROLITE 963”.
Perforation Process
A coated self-supporting substrate, as prepared in the General Procedure for Making a Ceramic Fiber Burner Plate, was perforated with the desired pattern using a laser (LasX Industries Incorporated of White Bear Lake, Minn., under the trade name “LASERSHARP” Laser Processing Module (LPM); 2500 W CO₂laser; 3 axis scanning module and the laser beam were run at speeds from 500 to 800 mm/sec) to form a burner plate.
Application of Organic Water Repellent Coating
The above burner plate was further dip coated with a polytetrafluoroethylene (PTFE) dispersion (available from Dyneon LLC, Aston, Pa. under the trade designation “TF-5060-RG”; diluted 3 parts deionized water to 1 part “TF-5060-RG”). The wet coated burner plate was placed on a perforated steel plate in a forced air furnace (obtained from Despatch Industries, Minneapolis, Minn., under the trade designation “DESPATCH V SERIES”) and dried for 30 minutes at 90° C., yielding a burner plate with an add-on of 50-60 weight percent “TF-5060-RG”.
Application of Wash Coat
“NALCO 1050” as received: The procedure described above for Application of Organic Water Repellent Coating was followed with the exception that a silica dispersion (available under the trade designation “NALCO 1050” from Nalco, Naperville, Ill.) was substituted for “TF-5060-RG” and the resulting wet coated/perforated ceramic substrate was dried for 3 hours at 80° C.
“NALCO 1050” diluted: The procedure described above for “NALCO 1050” as received was followed with the exception that 1 part “NALCO 1050” was diluted with 1 part deionized water.
“NALCO 2329” as received: The procedure described above for “NALCO 1050” as received was followed with the exception that a silica dispersion (available under the trade designation “NALCO 2329” from Nalco, Naperville, Ill.) was substituted for “NALCO 1050”.
“NALCO 2329” diluted: The procedure described above for “NALCO 2329” as received was followed with the exception that 1 part “NALCO 2329” was diluted with 1 part deionized water.
Burner Evaluation Test
A burner plate (6 in×6 in (15 cm×15 cm) piece) to be tested was mounted on burner housing of a test burner available from Heatco, Inc., Acworth, Ga., under the trade designation “PREMIX TEST FIRE STATION”. The burner was lit, and the gas and airflows were adjusted to produce uniform flame retention in radiant and blue-flame modes. The “turn down ratio” (i.e., the difference between the highest gas/air flow rate and the lowest gas/air flow rate at which the burner operates without flame-out) was determined by ascertaining the maximum and minimum stable flame conditions that could be obtained by modulating the gas/air flow rate.

Example 1

Using the Burner Evaluation Test described above, the burner plate having a “MICROLITE 963” coating as described above, in blue-flame mode, exhibited stable flame retention without flash back, and had a high turn down ratio.

Example 2

Using the Burner Evaluation Test described above, the burner plate having both “MICROLITE 963” and “TF-5060-RG” coatings as described above, in blue-flame mode, exhibited stable flame retention without flash back, and had a high turn down ratio.

Example 3

Using the Burner Evaluation Test described above, the burner plate having both “MICROLITE 963” and “NALCO 1050” as received coatings as described above, in blue-flame mode, exhibited stable flame retention without flash back, and had a high turn down ratio.

Example 4

Using the Burner Evaluation Test described above, the burner plate having both “MICROLITE 963” and “NALCO 1050” diluted coatings as described above, in blue-flame mode, exhibited stable flame retention without flash back, and had a high turn down ratio.

Example 5

Using the Burner Evaluation Test described above, the burner plate having both “MICROLITE 963” and “NALCO 2329” as received coatings as described above, in blue-flame mode, exhibited stable flame retention without flash back, and had a high turn down ratio.

Example 6

Using the Burner Evaluation Test as described above, the burner plate having both “MICROLITE 963” and “NALCO 2329” diluted coatings as described above, in blue-flame mode, exhibited stable flame retention without flash back, and had a high turn down ratio.
Foreseeable modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention. This invention should not be restricted to the embodiments that are set forth in this application for illustrative purposes.

Claims

1. A burner plate comprising

a self-supporting substrate having perforations extending through the substrate, the substrate comprising ceramic fibers and an inorganic oxide coating comprising inorganic oxide platelets selected from the group consisting of vermiculite platelets, mica platelets, talc platelets, and combinations thereof, on the substrate.

2. The burner plate according to claim 1 wherein the perforations comprise at least one of slits or circular holes.

3. The burner plate according to claim 1 wherein the burner plate is substantially planar.

4. The burner plate according to claim 1 wherein the perforations comprise less than 60% of the area of a top surface of the burner plate.

5. The burner plate according to claim 1 wherein the burner plate is non-planar.

6. The burner plate according to claim 1 further comprising a water repellant coating, a wash coat comprising a metal oxide or a metal non-oxide, catalytic materials, or combinations thereof.

7. The burner plate according to claim 1 wherein the vermiculite platelets are exfoliated vermiculite platelets.

8. The burner plate according to claim 1 wherein the ceramic fibers have an average length in a range of from 3 millimeters to 50 millimeters.

9. The burner plate according to claim 1 having a top surface and a bottom surface wherein the perforations have larger openings near the top surface than the openings near the bottom surface.

10. The burner plate according to claim 1 wherein the burner plate comprises at least about 75 percent by weight ceramic oxide fibers, based on the total fiber weight of the burner plate.

11. The burner plate according to claim 6 wherein the water repellant coating comprises polytetrafluoroethylene.

12. The burner plate according to claim 6 wherein the metal oxide or non-metal oxide is selected from the group consisting of aluminum oxide, zirconium oxide, silicon carbide, silicon oxide, titanium dioxide, and combinations thereof.

13. The burner plate according to claim 6 wherein the catalytic materials comprise materials selected from the group consisting of platinum, palladium, rhodium, iron, nickel, silver, ruthenium, copper, gold, iron oxide, copper oxide, alkaline earth oxides, and alkaline earth aluminates, rare earth oxides, rare earth aluminates, cerium oxide, vanadium oxide, manganese oxide, cobalt oxide, oxides having perovskite and perovskite-related crystal structures, metal phosphates and phosphate-oxide mixtures, rhodium supported on alumina, ceria, or alumina-ceria, and combinations thereof

14. A burner assembly comprising

a housing having a plenum chamber;

a gas inlet port connected to the housing; and

a burner plate covering the plenum chamber, wherein the burner plate comprises a self-supporting substrate having perforations extending through the substrate, the substrate comprising ceramic fibers and an inorganic oxide coating comprising inorganic oxide platelets selected from the group consisting of vermiculite platelets, mica platelets, talc platelets, and combinations thereof, on the substrate.

15. A burner assembly according to claim 14 wherein the burner plate is planar.

16. A burner assembly according to claim 14 wherein the burner plate has a shape selected from the group consisting of a cone, a sheet, a cylinder, and a thimble.

17. A burner assembly according to claim 14 wherein the burner assembly is a radiant burner assembly.

18. A burner assembly according to claim 14 wherein the burner assembly is a blue flame burner assembly.

19. A burner assembly according to claim 14 wherein the perforations in the burner plate comprise at least one of slits or circular holes.

20. A burner assembly according to claim 14 wherein the burner plate further comprises a water repellant coating, a wash coat comprising a metal oxide or a metal non-oxide, catalytic materials, or combinations thereof.