Patent Application
20130168470
Burner tips are found in furnaces, boilers, burners, incinerators and the like, and are used in the generation of power, steam, heating, production of petrochemicals, kilns, converting other products, and the like. Burner tips are also used in common household appliances, such as in household gas fired heating systems. Hot air and/or ignited fuel is dispensed through the burner tips, into a combustion chamber, from external fuel sources such as coal, natural gas, biomass, oil, hydrocarbons, and the like. Under these general circumstances the mixture of fuels cause ignition in the combustion chamber or a pilot light is used to ignite the fuels. The burner tips are in thermal communication with the exterior surface of boiler tubes, where present, in order to maintain or generate elevated temperatures within the fluid present in the boiler tubes, such as in facility boiler heater systems. The burner tips may also be in thermal communication with products in petrochemical, iron and steel, hydrocarbon processings, kilns and all similar type facilities. The term “fuel” includes pulverized solids, such as coal, natural gas, solid biofuels, other petroleum products and waste which are commonly used in the generation of power and heat. The term “fluid” includes fuel, air, water, and the like.
The environment within the combustion chamber can be extremely corrosive and abrasive. The burner tips employed in the combustion chamber are commonly exposed to highly abrasive and corrosive environments. Exposure of the burner tips to such environments often has the result of premature failure resulting in maintenance and boiler downtime costs to replace failed tips. As a regular course of business, the burner tips may be replaced according to a regular schedule. Soot and slag attach to the burner tips requiring cleaning, which also results in deterioration of the tubes. In any case, burner tips are subject to failure due to the hostile environment of the combustion chamber, and must be replaced. The burner tips can also increase or decrease certain air emission compounds depending upon their design, fuel and optimal temperatures.
Some burner tips are used in very hostile environments. For example, coal fuel power plants use burner tips in combustion chambers, which are exposed to high temperatures under and abrasion of high velocity coal particles and slag accumulation. The exposed hard faced surface of steel plates develop rough surfaces which increases eddy current to the coal laden stream, thus reducing the performance of the burner. These eddy currents increases wear, because the stream is not moving in laminar flow, as well as effecting combustion dynamics and increased emissions. Burner tips are also corroded by the flow.
Also solid waste/garbage incinerators used in the generation of energy utilize burner tips within a combustion chamber. The high cost of energy has led industry to extract usable heat from all high thermal value waste streams.
Burner tips used in large industrial furnaces may use either liquid fuel or gas. Liquid fuel burner tips may mix the fuel with steam prior to combustion to atomize the fuel to enable more complete combustion and combustion air is mixed with the fuel at the zone of combustion. Gas fired burner tips can generally be classified as either premix or raw gas, depending on the method used to combine the air and fuel. They also differ in configuration and the type of burner tip used. Raw gas burner tips inject fuel directly into the air stream, and the mixing of fuel and air occurs simultaneously with combustion. Many raw gas burners produce luminous flames. Premix burner tips, on the other hand, mix some or all of the fuel with some or all of the combustion air prior to combustion. Since premixing is accomplished by using the energy present in the fuel stream, airflow is largely proportional to fuel flow.
Burner tips are known, and come in a large variety of shapes and sizes. The burner tip is used to inject a fuel and control gas into a combustion zone. In general, burner parameters can be varied including the number, location, size, and configuration of the fuel tips. Domestic heaters may use only one burner tip while industrial boilers may use multiple pairs or larger groups of parallel burner tips.
U.S. Pat. No. 5,178,921 issued to Whelan on Jan. 12, 1993 shows a burner block assembly and material comprising two layers including a relatively thick exterior shell comprising a refractory material which has fibrous alumina and silica and an internal bore, a relatively thin erosion resistant liner in the bore which has a fabric matrix of woven ceramic fibers with insulating properties and silicon carbide particles supported by and coating the fabric matrix.
U.S. Pat. No. 2,933,259 issued to Raskin on Apr. 19, 1960 shows a nozzle head that may be used as a burner tip in burner equipment for atomizing a liquid fuel or for mixing a gaseous fuel with air or other combustive. It could also be used to produce a spray of any liquid such as a fine water spray or a spray of fine solid material such as pulverized coal. U.S. Pat. No. 4,490,171 issued to Suzuki et al. on Dec. 25, 1984 and assigned to Kobe Steel, Limited also discloses a method and apparatus for injecting pulverized fuel into a blast furnace.
Likewise, U.S. Pat. No. 6,112,676 issued to Okazaki et al. on Sep. 5, 2000 and assigned to Hitachi, Ltd and Babcock Hitachi K.K. describes a pulverized coal burner which includes a pulverized coal nozzle for jetting a mixture of pulverized coal and primary air, a secondary air nozzle and a tertiary air nozzle, concentrically arranged around the outer periphery of the pulverizes coal nozzle, and a tube expanded portion at the end of a partition wall separating two adjacent air nozzles. U.S. Pat. No. 5,535,686 issued to Chung on Jul. 16, 1996 discloses a burner for a tangentially fired boiler having a pivotally mounted burner tip attached to a fuel passage that in operation, conveys pulverized coal carried by an air stream.
U.S. Pat. No. 4,499,945 issued to Hill et al. on Feb. 19, 1985 and assigned to the U.S. Department of Energy discloses a silane-propane igniter/burner that is used in underground coal gasification. The silane spontaneously ignites on contact with oxygen and burns the propane fuel, which ignites the coal. U.S. Pat. No. 6,315,551 issued to Salzsieder et al. on Nov. 13, 2001 and assigned to Entreprise Generale de Chauffage Industriel Pillard describes burners having at least three air feed ducts, including an axial air duct and a rotary air duct concentric with at least one fuel feed, and central stabilizer. U.S. Pat. No. 6,902,390 issued to Spicer on Jun. 7, 2005 and assigned to ExxonMobil Chemical Patents, Inc. discloses a burner tip for pre-mix burners for use in combusting fuel in burners used in furnaces such as those found in steam cracking for petrochemical applications.
U.S. Pat. No. 4,505,665 issued to Mansour on Mar. 19, 1985 and assigned to Southern California Edison discloses a method and angle adjustable burner tip for suppressing emissions of nitrogen oxides when burning a fuel in a combustion chamber containing a flame zone. U.S. Pat. No. 4,702,691 issued to Ogden on Oct. 27, 1987 and assigned to John Zink Company describes an even flow radial burner tip used in a furnace. U.S. Pat. No. 4,601,428 issued to Kurogo on Jul. 22, 1986 and assigned to Tokyo Sangyo Kabushiki Kaisha discloses a burner tip, which has a tapered body having a hollow conical interior, that is used for boilers, heating furnaces, melting furnaces and other burning apparatus to promote the mixing of a liquid fuel with such spraying medium as air or steam, and provides the fine granulation of the liquid fuel and the combustion of the fuel.
An example of a combustion chamber with burner tips extending into the combustion chamber is disclosed in U.S. Pat. No. 6,220,188, which was issued to Boutrup on Apr. 24, 2001 and assigned to Burmeister & Wain Energi A/S. The '188 patent discloses a windbox burner having burner tips for use in large furnace plants, such as refuse incineration plants or steam boilers, it is common that one or more windboxes for supply of combustion air are provided on the front wall of the boiler. Each windbox comprises several windbox burners, each capable of containing, for example, a combined coal/oil burner. Coaxially with and enclosing the coal/oil burner one or more pipes are provided for supplying air to the burner tip, which air supply pipes are enclosed by a substantially tubular register casing having openings that permit combustion air from the windbox to flow into one or more of the air supply pipes.
The present invention is drawn to innovative metallic burner tips used in improved combustion chamber, typically found in utility, power generation and similar furnaces, and furnaces in petrochemical/refinery, biomass, kilns, and riton and steel production burner systems, for example, and improved components thereof. Burner tips are also used in the petrochemical industry, power generation, boilers, baking ovens, grills, and other cooking apparatuses. All heat/combustion applications utilizing natural gas, oxygen/natural gas, and petroleum also use burner tips. The combustion chambers, of the present invention, contain burner tips and/or plenum composed of metal having a thermal protective layer on at least one unexposed surface thereof. The thermal protective layer need not be disposed on the exposed surface, and functions through the substrate. In other words, the heat may be applied to the uncoated exposed surface, while the unexposed surface is coated, and the same benefit is derived. This is the case because the thermal protective coating acts to modify the thermal wavelengths instead of directly insulating the surface.
The plena carry combustible fluids, including pulverized coal, and extend into the combustion chamber with the burner tips. A thermal protective layer on the exposed surfaces of the burner tips, and plena within the combustion chamber of the present invention may contain from about 5% to about 40% of an inorganic adhesive taken from the group consisting of an alkali/alkaline earth metal silicate taken from the group consisting of sodium silicate, potassium silicate, calcium silicate, and magnesium silicate, from about 45% to about 92% of a filler, and from about 1% to about 20% of one or more emissivity agents, in a dry admixture. Preferably, a thermal protective layer of the present invention also contains from about 1% to about 5% of a stabilizer.
An aspect of the present invention is to extend the effective repair and replacement cycles all combustion chambers, especially burner tips and plenum, in all furnace applications. The overall cost of furnace applications is reduced by the concomitant reduction in maintenance costs.
The present invention extends the effective lifespan of conventional burner tips, plenum, and auxiliary components. Further, the burner tips need not be coated on the outside but may instead be coated on the internal surfaces of the burner tips and plenum so that less coating needs to be used. To coat the internal surface, the present design merely needs to feed the spray coating through the internal passage of the burner tips and plenum. A single thermal protective layer disposed on a surface of the metallic substrate that is not directly exposed to elevated heat maintains functionality.
An aspect of the present invention is to reduce the clogging of burner tips having narrower openings by reducing the amount of slag and soot build up thereby reducing the amount of time required to clean and repair the tips for continued use.
Another aspect of the present invention is to reduce certain air emissions such as oxidation of nitrogen.
These and other aspects of the present invention will become readily apparent upon further review of the following drawings and specification.
The novel features of the described embodiments are specifically set forth in the appended claims; however, embodiments relating to the structure and process of making the present invention, may best be understood with reference to the following description and accompanying drawings.
Similar reference characters denote corresponding features consistently throughout the attached drawings.
A burner tip 12, as shown in alternative embodiments in
The thermal protective layer 22 may be disposed on the external surface 16 of the burner tip 12 support layer 14, the internal surface 18 of the burner tip 12 support layer 14 in which the inner surface 18 is not directly exposed to the flame, or the internal and external surfaces 16 and 18 of the burner tip 12 support layer 14. Alternatively, the thermal protective layer 22 may be disposed on merely part of a surface 16 and/or 18. The support layer 14 comprises a metallic substrate. The metallic substrate is taken from the group consisting of iron, aluminum, alloys, steel, and cast iron. A plenum 24 may extend from the burner tip 12, and may have a thermal protective layer 22 disposed on an internal or external surface 16 and 18. The plenum 24 and the burner tip 12 may be fully continuous; alternatively, the plenum 24 may be connected to but separate from the burner tip 12. In some embodiments, a plenum 24 is not exposed to the combustion chamber.
In alternative embodiments, such as shown in
An alternative embodiment of the present invention is shown in
Another alternative embodiment, as shown in
The present invention is not seen to be limited to the configurations of burner tips 12 shown, but includes burner tips 12 of a various designs and sizes. The burner tips 12 of the present invention are seen to include embodiments used in household applications as well as those you for commercial, municipal and industrial applications.
The thermal protective layer may be applied as a high emissivity thermal protective coating. Suitable coatings and methods of application are described in U.S. Pat. No. 7,105,047 issued on Sep. 12, 2006 and assigned to Wessex Incorporated, the contents of which are incorporated herein in their entirety.
A high emissivity coating suitable for forming the thermal protective layer on the exposed surfaces of the combustion chamber including burner tips, and plena of the present invention may contain from about 5% to about 30% of an inorganic adhesive, from about 45% to about 92% of a filler, and from about 2% to about 20% of one or more emissivity agents, in a dry admixture. Preferably, the dry admixture also contains from about 1% to about 5% of a stabilizer. In a coating solution according to the present invention, a wet admixture of the thermal protective coating contains from about 6% to about 40% of an inorganic adhesive, from about 23% to about 46% of a filler, from about 1% to about 10% of one or more emissivity agents, and from about 18% to about 50% water. In order to extend the shelf life of the coating solution, from about 0.5% to about 2.5% of a stabilizer is preferably added to the wet admixture. The wet admixture coating solution contains between about 40% and about 60% total solids.
As used herein, all percentages (%) are percent weight-to-weight, also expressed as weight/weight %, % (w/w), w/w, w/w % or simply %, unless otherwise indicated. Also, as used herein, the terms “wet admixture” refers to relative percentages of the composition of the thermal protective coating in solution and “dry admixture” refers to the relative percentages of the composition of the dry thermal protective coating mixture prior to the addition of water. In other words, the dry admixture percentages are those present without taking water into account. Wet admixture refers to the admixture in solution (with water). “Wet weight percentage” is the weight in a wet admixture, and “dry weight percentage” is the weight in a dry admixture without regard to the wet weight percentages.
The inorganic adhesive is preferably an alkali/alkaline earth metal silicate taken from the group consisting of sodium silicate, potassium silicate, calcium silicate, and magnesium silicate. The filler is preferably a metal oxide taken from the group consisting of silicon dioxide, aluminum oxide, titanium dioxide, magnesium oxide, calcium oxide and boron oxide. The emissivity agent is preferably taken from the group consisting of silicon hexaboride, carbon tetraboride, silicon tetraboride, silicon carbide, molybdenum disilicide, tungsten disilicide, zirconium diboride, cupric chromite, and metallic oxides such as iron oxides, magnesium oxides, manganese oxides, copper chromium oxides, chromium oxides, cerium oxides, terbium oxides, and derivatives, and combinations thereof. The copper chromium oxide, as used in the present invention, is a mixture of cupric chromite and cupric oxide. The stabilizer may be taken from the group consisting of bentonite, kaolin, magnesium alumina silica clay, tabular alumina, and stabilized zirconium oxide. The stabilizer is preferably bentonite. Other ball clay stabilizers may be substituted herein as a stabilizer.
Coloring may be added to the protective coating layer of the present invention to depart coloring to the burner tips. Inorganic pigments may be added to the protective coating without generating toxic fumes. In general, inorganic pigments are divided into the subclasses: colored (salts and oxides), blacks, white and metallic. Suitable inorganic pigments include but are not limited to yellow cadmium, orange cadmium, red cadmium, deep orange cadmium, orange cadmium lithopone, and red cadmium lithopone.
A preferred embodiment of the present invention contains a dry admixture of from about 10% to about 25% sodium silicate, from about 50% to about 79% silicon dioxide powder, and from about 4% to about 15% of one or more emittance agent(s) taken from the group consisting of iron oxide, boron silicide, boron carbide, silicon tetraboride, silicon carbide, molybdenum disilicide, tungsten disilicide, zirconium diboride. Preferred embodiments of the thermal coating may contain from about 1.0% to about 5.0% bentonite powder in dry admixture. The corresponding coating in solution (wet admixture) for this embodiment contains from about 20.0% to about 35.0% sodium silicate, from about 25.0% to about 50.0% silicon dioxide, from about 18.0% to about 39.0% water, and from about 2.0% to about 7.5% one or more emittance agent(s). This wet admixture must be used immediately. In order to provide a coating solution admixture (wet admixture), which may be stored and used later, preferred embodiments of the thermal coating contain from about 0.50% to about 2.50% bentonite powder. Preferably deionized water is used. Preferred embodiments of the wet admixture have a total solids content ranging from about 45% to about 55%.
A preferred thermal protective coating of the present invention contains a dry admixture from about 15.0% to about 20% sodium silicate, from about 69.0% to about 79.0% silicon dioxide powder, about 1.00% bentonite powder, and from about 5.00% to about 15.0% of an emittance agent. The emittance agent is taken from one or more of the following: iron oxide, boron silicide, and boron carbide.
A most preferred wet admixture contains about 20.0% sodium silicate based on a sodium silicate solids content of about 37.45%, from about 34.5% to about 39.5% silicon dioxide powder, about 0.500% bentonite powder, and from about 2.50% to about 7.5% of an emittance agent, with the balance being water. The emittance agent is most preferably taken from the group consisting of iron oxide, boron silicide, and boron carbide (also known as, carbon tetraboride). Preferred embodiments include those where the emittance agent comprises about 2.50% iron oxide, about 2.50% boron silicide, or from about 2.50% to about 7.50% boron carbide. The pH of a most preferred wet admixture according to the present invention is about 11.2.+−.1.0, the specific gravity is about 1.45.+−.0.05 and the total solids content is about 50.+−.0.3%.
An inorganic adhesive, which may be used in the present invention, includes N (trademark) type sodium silicate that is available from the PQ Corporation (of Valley Forge, Pa.). Sodium silicate, also known as waterglass, is a versatile, inorganic chemical made by combining various ratios of sand and soda ash (sodium carbonate) at high temperature. Sodium silicates (Na2O.XSiO2) are metal oxides of silica. All soluble silicates can be differentiated by their ratio, defined as the weight proportion of silica to alkali (SiO2/Na2O). Ratio determines the physical and chemical properties of the coating. The glassy nature of silicates imparts strong and rigid physical properties to dried films or coatings. Silicates air dry to a specific moisture level, according to ambient temperature and relative humidity. Heating is necessary to take these films to complete dryness—a condition in which silicates become nearly insoluble. Reaction with other materials, such as aluminum or calcium compounds, will make the film coating completely insoluble. The N (trademark) type sodium silicate, as used in the examples below, has a weight ratio SiO2/Na2O is 3.22, 8.9% Na2O, 28.7% SiO2, with a density (at room temperature of 20° C.) of 41.0° Be′, 11.6 lb/gal or 1.38 g/cm3. The pH is 11.3 with a viscosity of 180 centipoises. The N type sodium silicate is in a state of a syrupy liquid.
The term “total solids” refers to the sum of the silica and the alkali. The weight ratio is a most important silicate variable. Ratio determines the product solubility, reactivity and physical properties. Ratio is either the weight or molar proportion of silica to alkali. Density is an expression of total solids and is typically determined using a hydrometer or a pycnometer.
The filler may be a silicon dioxide powder such as Min-U-Sil (trademark) silicon dioxide available from U.S. Silica (of Berkeley Springs, W. Va.). This silicon dioxide is fine ground silica. Chemical analysis of the Min-U-Sil (trademark) silicon dioxide indicates contents of 98.5% silicon dioxide, 0.060% iron oxide, 1.1% aluminum oxide, 0.02% titanium dioxide, 0.04% calcium oxide, 0.03% magnesium oxide, 0.03% sodium dioxide, 0.03% potassium oxide and a 0.4% loss on ignition. The typical physical properties are a compacted bulk density of 41 lbs/ft3, an uncompacted bulk density of 36 lbs/ft3, a hardness of 7 Mohs, hegman of 7.5, median diameter of 1.7 microns, an oil absorption (D-1483) of 44, a pH of 6.2, 97%-5 microns, 0.005%+325 Mesh, a reflectance of 92%, a 4.2 yellowness index and a specific gravity of 2.65.
Emittance agents are available from several sources. Emissivity is the relative power of a surface to emit heat by radiation, and the ratio of the radiant energy emitted by a surface to the radiant energy emitted by a blackbody at the same temperature. Emittance is the energy radiated by the surface of a body per unit area.
The boron carbide (B4C), also known as carbon tetraboride, which may be used as an emissivity agent in the present invention, is available from Electro Abrasives (of Buffalo, N.Y.). Above 1300° C., it is even harder than diamond and cubic boron nitride. It has a four point flexural strength of 50,000 to 70,000 psi and a compressive strength of 414,000 psi, depending on density. Boron Carbide also has a low thermal conductivity (29 to 67 W/mK) and has electrical resistivity ranging from 0.1 to 10 ohm-cm. Typical chemical analysis indicates 77.5% boron, 21.5% carbon, iron 0.2% and total Boron plus Carbon is 98%. The hardness is 2800 Knoop and 9.6 Mohs, the melting point is 4262° F. (2350° C.), the oxidation temperature is 932° F. (500° C.), and the specific gravity is 2.52 g/cc.
Green silicon Carbide (SiC), an optional emissivity agent, is also available from Electro Abrasives. Green Silicon Carbide is an extremely hard (Knoop 2600 or Mohs 9.4) man made mineral that possesses high thermal conductivity (100 W/m-K). It also has high strength at elevated temperatures (at 1100° C., Green SiC is 7.5 times stronger than Al2O3). Green SiC has a Modulus of Elasticity of 410 GPa, with no decrease in strength up to 1600° C., and it does not melt at normal pressures but instead dissociates at 2815.5° C. Green silicon carbide is a batch composition made from silica sand and coke, and is extremely pure. The physical properties are as follows for green silicon carbide: the hardness is 2600 Knoop and 9.4 Mohs, the melting point is 4712° F. (2600° C.), and the specific gravity is 3.2 g/cc. The typical chemical analysis is 99.5% SiC, 0.2% SiO2, 0.03% total Si, 0.04% total Fe, and 0.1% total C. Commercial silicon carbide and molybdenum disilicide may need to be cleaned, as is well known in the art, to eliminate flammable gas generated during production.
Boron silicide (B6Si) is available from Cerac (of Milwaukee, Wis.). The boron silicide, also known as silicon hexaboride, available from Cerac has a −200 mesh (about 2 microns average) and a typical purity of about 98%. Zirconium boride (ZrB2) is also available from Cerac with a typical average of 10 microns or less (−325 mesh), and a typical purity of about 99.5%. Iron oxide available from Hoover Color (of Hiwassee, Va.) is a synthetic black iron oxide (Fe2O3) which has an iron oxide content of 60%, a specific gravity of 4.8 gm/cc, a tap density (also known as, bulk density) of 1.3 gm/cc, oil absorption of 15 lbs/100 lbs, a 325 mesh residue of 0.005, and a pH ranging from 7 to 10.
The admixture may include bentonite powder, tabular alumina, or magnesium alumina silica clay. The bentonite powder permits the coating to be prepared and used at a later date. Otherwise, the coating must be applied to the support layer as soon as mixed. The examples provided for the present invention include PolarGel bentonite powder available from Mineral and Pigment Solutions, Inc. (of South Plainfield, N.J.). Bentonite is generally used for the purpose of suspending, emulsifying and binding agents, and as rheological modifiers. The typical chemical analysis is 59.00% to 61.00% of silicon dioxide (SiO2), 20.00% to 22.00% of aluminum oxide (Al2O3), 2.00% to 3.00% calcium oxide (CaO), 3.50% to 4.30% magnesium oxide (MgO), 0.60% to 0.70% ferric oxide (Fe2O3), 3.50% to 4.00% sodium oxide (Na2O), 0.02% to 0.03% potassium oxide (K2O), and 0.10% to 0.20% titanium dioxide and a maximum of 8.0% moisture. The pH value ranges from 9.5 to 10.5. Typical physical properties are 83.0 to 87.0 dry brightness, 2.50 to 2.60 specific gravity, 20.82 pounds/solid gallon, 0.0480 gallons for one pound bulk, 24 ml minimum swelling power, maximum 2 ml gel formation, and 100.00% thru 200 mesh. Tabular alumina and magnesium alumina silica clay are also available from Mineral and Pigment Solutions, Inc.
Colorants, which may be added to the present invention, include but are not limited to inorganic pigments. Suitable inorganic pigments, such as yellow iron oxide, chromium oxide green, red iron oxide, black iron oxide, titanium dioxide, are available from Hoover Color Corporation. Additional suitable inorganic pigments, such as copper chromite black spinel, chromium green-black hematite, nickel antimony titanium yellow rutile, manganese antimony titanium buff rutile, and cobalt chromite blue-green spinel, are available from The Shepherd Color Company (of Cincinnati, Ohio).
A surfactant may be added to the wet admixture prior to applying the thermal protective layer to the burner tip or plenum. The surfactant was Surfynol (trademark) available from Air Products and Chemicals, Inc. (of Allentown, Pa.). The Surfyonol (trademark) has a chemical structure of ethoxylated 2,4,7,9-tetramethyl 5 decyn-4,7-diol. Other surfactants may be used, such as STANDAPOL (trademark) T, INCI which has a chemical structure of triethanolamine lauryl sulfate, liquid mild primary surfactant available from Cognis-Care Chemicals (of Cincinnati, Ohio). The amount of surfactant present by weight in the wet admixture in from about 0.05% to about 0.2%.
The present invention is applied to a surface of the burner tip. The burner tip surface may be a metallic substrate such as iron, aluminum, alloys, steel, carbon steel, cast iron, stainless steel and the like. The coating is typically applied wet, and either allowed to air dry or heat dry. The metal substrates may be internal and/or external surfaces of burner tips and plenum which may be subjected to high temperatures.
The coating is typically applied directly to the support layer 14 of the burner tip 12 and/or plenum 24. The preparation of the tube shield support layer 14 involves surface preparation, preparation of thermal protective coating, and application of the thermal protective coating to the surface of the support layer 14 of the burner tip 12 and/or plenum 24. First, preparation of the surface occurs. The surface is prepared first by grit basting and then cleaning the surface. Grit blasting is desirable to remove oxidation and other contaminants. Grit media should be chosen depending on metal type, and may include aluminum oxide, glass beads, black beauty, and the like.
Gun pressure will vary depending on the cut type, condition of the metal and profile desired; very old metal requires 60-80 psi while newer metal may only require 40-60 psi. Oil free air should be used. The surface then cleaned after the grit blasting, the surface should be thoroughly cleaned to remove all loose particles with air blasts. Acetone can also be used on a clean cloth to wipe the surface clean. Acetone should be used under proper ventilation and exercising all necessary precautions. A cleaning compound may be used on certain stainless steel surfaces in lieu of grit blasting.
After the grit blast, the metal surface of the support layer 14 should be thoroughly cleaned to remove all loose particles with clean oil and water free air blasts. Avoid contaminating surface with fingerprints. Acetone can be used (under proper ventilation and exercising all necessary precautions when working with acetone) on a clean cloth to wipe the surface clean. A cleaning compound may be used on certain stainless steel in lieu of grit blasting. Dur-lum available from Blue Wave Ultrasonics (of Davenport, Iowa), a powdered alkaline cleaner, may be used in cleaning metal surface instead of, or in addition to, acetone.
When using the wet admixture containing a stabilizer, solids may settle during shipment or storage. Prior to use all previously mixed coating must be thoroughly re-mixed to ensure all settled solids and clumps are completely re-dispersed. When not using a stabilizer, the coating may not be stored for any period of time. In any case, the coating should be used immediately after mixing to minimize settling.
Mixing instructions for one and five gallon containers. High speed/high shear saw tooth dispersion blade 5″ diameter for one gallon containers and 7″ diameter for five gallon containers may be attached to a hand drill of sufficient power with a minimum no load speed of 2000 rpm shear. Dispersion blades can be purchased from numerous suppliers. Mix at high speed to ensure complete re-dispersion for a minimum of 30 minutes.
The product should be applied directly after cleaning a metal surface so minimal surface oxidation occurs. The product should be applied in a properly ventilated and well lit area, or protective equipment should be used appropriate to the environment, for example within the combustion chamber 10. The mixed product should not be filtered or diluted. If the product is only applied to the unexposed inner passageways of the burner tips, or the plenum, then less danger of exposure to the fumes may exist.
A high volume low pressure (HVLP) spray gun should be used with 20-40 psi of clean, oil and water free air. Proper filters for removal of oil and water are required. Alternatively, an airless spray gun may be used. Other types of spray equipment may be suitable. The applicator should practice spraying on scrap metal prior to spraying the actual part to ensure proper coverage density. Suitable airless spray systems are available from Graco (of Mineapolis, Minn.). Suitable HVLP spray systems, which are desirable for metal/alloy process tubes, are available from G.H. Reed Inc. (of Hanover, Pa.). A high speed agitator may be desirable. Suitable spray gun tips may be selected to provide the proper thickness without undue experimentation.
Controlling the coverage density may be critical to coating performance. Dry coating thickness should be from about two (2) mils (about 50 microns (O) to about ten (10) mils (about 255 μl), depending upon typed, size and condition of substrate. One (1) mil equals 25.4 μl. Proper thickness may vary. If possible, rotate the part 90 degrees at least once to maintain even coverage. Allow 1 to 4 hours of dry time before the part is handled, depending upon humidity and temperature.
The burner tips and/or the plenum at the very least have a thermal protective layer on an internal surface thereof, but may also have the thermal protective layer disposed on the entire surface, or on both the external and internal surfaces. The external surfaces of the burner tips and/or plenum are exposed to the combustion chamber; while the internal surfaces are not. The internal surface of the burner tips are enclosed within the burner tips and includes the passages therein. The internal surface of the plenum is enclosed within the plenum. The present invention is seen to include all types of burner tips, including the plenum, having a protective layer, according to the present invention, on at least one surface thereof.
Prior to application of a thermal protective coating to the prepared surface, the thermal protective coating should be thoroughly remixed to ensure all settled solids and clumps are completely redispersed. Also, the remixed thermal protective coating should be used promptly after remixing to minimize settling. To mix, a high speed/high shear dispersion blade should be attached to a hand drill of sufficient power with a minimum speed of 2300 rpm. Dispersion blades can be purchased from numerous suppliers. The thermal protective coating is prepared by mixing at high speed while moving the blade up and down inside the coating's container to ensure complete redispersion for a minimum of 10 minutes. Alternative equivalent mixing procedures may be used.
It is desirable to apply the thermal protective coating to the surface directly after cleaning the surface so minimal surface oxidation occurs. The prepared surface should be at, or near, room temperature (60° F. to 80° F.) and humidity should be below 50%, if possible.
Spray equipment which may be used include a high volume low pressure (HPLV) spray gun, which should be used with 20-40 psi of clean, oil free air. Other types of spray equipment may be suitable, as well, including airless spray equipment. Controlling the coverage density is desirable to enhance coating performance. If possible, the support layer 30, or the spray equipment, should be rotated 90 degrees at least once to maintain even coverage. Never reapply after the coat has completely dried. Allow 2 to 4 hours of dry time before the shield 12, 14, 15, or 17 is handled depending upon humidity and temperature.
Example 1 contains N grade Sodium Silicate 15.0% dry weight and 20.0% wet weight based on sodium silicate solids content of 37.45%, Min-U-Sil 5 SiO.sub.2 powder 79.0% dry weight and 39.5% wet weight, 1000 W B4C 5.00% dry weight and 2.50% wet weight, PolarGel bentonite powder (Item#354) 1.00% dry weight and 0.500% wet weight, and 37.5% water, based on sodium silicate solids content of 37.45%. The pH of example 1 is 11.2.+−.1.0, the specific gravity is 1.45.+−.0.05, and the total solids content is 50.+−.0.3%.
Example 1 may be prepared by placing the liquid ingredients in a clean, relatively dry mixing container. While mixing, the remaining ingredients are added slowly to the mixture to prevent the powders from clumping and sticking to the side of the mixing container. The mixture is then mixed at high power for at least 20 minutes depending on the configuration of the mixer. The mixing was carried out in a high shear mixer with a 2.5 inch Cowles Hi-Shear Impeller blade with a 0.5 horsepower motor generating 7500 rpm without load.
Example 2 contains N grade Sodium Silicate 15.0% dry weight and 20.0% wet weight based on sodium silicate solids content of 37.45%, min-U-Sil 5 SiO2 powder 69.0% dry weight and 34.5% wet weight, 1000 W B4C 15.0% dry weight and 7.5% wet weight, PolarGel bentonite powder (Item#354) 1.00% dry weight and 0.500% wet weight, and 37.5% water, based on sodium silicate solids content of 37.45%. The pH of example 2 is 11.2±1.0, the specific gravity is 1.45±0.05, and the total solids content is 50±0.3%. Example 2 is prepared in the same fashion as example 1. This embodiment is a preferred embodiment for sintering applications. Example 2 may be prepared in the same manner as Example 1.
A burner tip was coated with the composition of example 1 and observed under real-life circumstances. The coated burner tips were disposed in the super-heater of a CE, VU40, coal fired, 65MW unit with tangential burner tips (no tilts). The burner tips for the coal fired unit were compared where one burner tip, a stainless steel low-NOX burner tip was left uncoated and one identical burner tip had the thermal protective layer disposed thereon. The uncoated tip failed after six (6) months with the temperature of the tip in excess of 2000° F. The stainless steel low-NOX burner tip continues to be used after two (2) years with the temperature of the tip being 300° F.
It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.
This application is a continuation-in-part of, and further claims the benefit of, U.S. application Ser. No. 12/243,916 entitled “BURNER TIPS” filed on 1 Oct. 2008, the contents of which are incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12243916 | Oct 2008 | US |
| Child | 13495940 | US |
