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  Combustion method and burner head, burner comprising one such burner head, and boiler comprising one such burner headUSPTO Application #: 20060147854Title: Combustion method and burner head, burner comprising one such burner head, and boiler comprising one such burner head Abstract: A burner head has at least two and preferably four openings (45) in an aperture plate (37), with uniformly inclined guide blades (23) for the delivery of incoming air in the direction of an axis (31) to a combustion chamber (15) in the form of incoming air jets (53) intersecting one another in the chamber. Between the openings (45), blocking blades (27) are embodied, for forming peripheral underpressure zones (55) between the incoming air jets (53). The incoming air jets (53) are deflected by the guide blades (23) into a position that is inclined relative to the axis (31). The incoming air jets (53) therefore diverge and as a result create a central underpressure zone (57) about the axis (31) between the incoming air jets (53). By means of the central underpressure zone and the inclination of the incoming air jets, a rotation of the incoming air is achieved. In operation of the burner, hot gases from outside are aspirated into the peripheral underpressure zones (55) and, counter to the flow direction of the incoming air, into the central underpressure zone (57) between the incoming air jets (53). These flow conditions create ideal conditions for the combustion of gaseous, liquid and/or particulate fuel in a calm, cool, low-polluting flame. This combustion is practically independent of the size and shape of the combustion chamber and of the pressure conditions in the combustion chamber, for combustion installations of 16 kW to 1000 kW, or more. (end of abstract) Agent: Buchanan Ingersoll PC (including Burns, Doane, Swecker & Mathis) - Alexandria, VA, US Inventor: Jorg Fullemann USPTO Applicaton #: 20060147854 - Class: 431009000 (USPTO) Related Patent Categories: Combustion, Process Of Combustion Or Burner Operation, Flame Shaping, Or Distributing Components In Combustion Zone, Whirling, Recycling Material, Or Reversing Flow In An Enclosed Flame Zone The Patent Description & Claims data below is from USPTO Patent Application 20060147854. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] In the conventional oil burner, the heating oil is injected at high pressure into the incoming air flowing into the combustion chamber. The difference in speed between the air and the oil droplets favors evaporation of the oil and thus leads to a reduction in the size of the oil droplet, until finally the difference in speed between the air and the oil droplets has vanished. As the speed decreases, the evaporated liquid around the droplet forms a mixture of fuel vapor and air with an increasing proportion of fuel vapor. The flammability of the mixture increases during the combustion process. Because of the heat in the flame that already exists in the burner, this increasingly more readily flammable mixture ignites. [0002] In yellow-flame burners, to prevent the flame from separating from the burner head, an underpressure one is created, centrally or annularly around a central region, with a blocking disk. A lesser quantity of incoming air, set into rotation, is delivered to this underpressure zone. The fuel is also injected into this underpressure zone. In this flame core, it burns under conditions of oxygen deficiency. Secondary air is delivered in relatively large quantity centrally and/or through an annular slot around this underpressure zone and allows the combustion of all the delivered fuel in an elongated flame. Thanks to the central underpressure zone and the supply of fresh air enveloping it, the flame core and hence the entire flame is aspirated against the blocking disk. The flame therefore persists downstream of the blocking disk and does not separate from it. [0003] In this combustion, however, a high flame temperature is reached. This high temperature on the one hand leads to carbonization of the fuel nozzle, which impairs the safety and reliability of operation, and on the other hand leads to favorable conditions for the combining of nitrogen from the air with oxygen from the air. In this kind of combustion, the result is an excessive concentration of nitrogen oxides (NOx). In this combustion, the flame is yellow. The yellow light is given off by glowing carbon, which is created by the decomposition of the fuel. [0004] It has been discovered that the concentration of the resultant nitrogen oxides is very strongly dependent on the combustion temperature. Each reduction of the temperature by 100.degree. C. reduces the NOx concentration to half the previous value. If it is possible to lower the combustion temperature by 300.degree. C., the NOx concentration is accordingly then only about 1/8 that of combustion with a yellow flame. [0005] Cooling the flame is attained by means of an excess of incoming air, a purposeful recirculation of exhaust gases, and/or a spatial separation of the evaporation zone and the mixing zone. [0006] To reduce NOx values in the flue gas in the combustion of heating oil, so-called blue-flame burners have been developed. With the blue-flame burners, the combustion zone is separated from the evaporation and mixing zone as much as possible. In the process, the fuel in the incoming air or in a mixture of incoming air and combustion gas is evaporated and thereafter combusted. In burners that make a virtually stoichiometric combustion possible, recirculation of the exhaust gases must be provided for. [0007] From European Patent Disclosure EP-A 0 321 809 (Brown Boveri AG), a method and a burner are known for the premix kind of combustion of liquid fuel in a burner. The burner has two complementary that put together make a hollow cone, and between which there are tangential air inlet slits. The hollow partial conical bodies have a conical inclination that increases in the flow direction. The cone axes of the partial conical bodies are spaced apart from one another, and between these cone axes there is a fuel nozzle, which injects a liquid fuel into the hollow cone at an angle that assures that the fuel does not wet the wall of the hollow cone. Through the tangential air inlet slits, air is delivery, which forms a jacket around the fuel fog and rotates around the fuel cone. In the region where the turbulence breaks up, that is, in the region of a central return-flow zone in the orifice region of the hollow cone, the fuel-air mixture reaches its optimal, homogeneous fuel concentration via the cross section of the turbulence. The ignition takes place at the tip of the return-flow zone. [0008] With this burner, the least pollutant emissions values are achieved when the evaporation is concluded before the entry into the combustion zone. This is equally true for combustion with an air excess of 60%, and if this air excess is replaced with recirculated exhaust gas. How the exhaust gases are recirculated cannot be learned from this reference. In designing the partial cone bodies in terms of their conical inclination and the width of the tangential air inlet slits, narrow limits must be adhered to, so that the desired flow pattern of the air with its return-flow zone in the region of the burner orifice for flame stabilization will be established. [0009] According to European Patent Disclosure EP-A 0 491 079 (Asea Brown Boveri AG), one disadvantage of this burner is that in some cases, it cannot be used by atmospheric combustion installations. This reference therefore proposes a burner head that has minimal pollutant emissions and in which, by the shaping of the burner head and the guidance of the incoming air through the burner, stabilization of the flame is established at the end of a premixing zone in the center and/or on the outer periphery of the combustion chamber. Evidently, the flame stability of the burner of EP-A 0 321 809 was inadequate. [0010] The burner head of EP-A 0 491 079 has a fuel lance with a fuel nozzle. An incoming air conduit is disposed around this fuel nozzle. On the downstream side, the fuel nozzle is closed off with an aperture plate. Disposed around this first incoming air conduit is a further incoming air conduit. This second incoming air conduit is provided, on the downstream side, with a number of guide devices. On the downstream side of the fuel nozzle is a combustion chamber, which in the downstream direction comprises a premixing pipe and an adjoining burnoff pipe whose diameter is larger than that of the premixing pipe. Flame stabilization can be achieved as needed by introducing an interference body downstream of the premixing zone. [0011] In operation of this burner, some of the incoming air is introduced via at least one aperture plate into a premixing zone located downstream of a fuel nozzle. Another portion of the incoming air, before flowing into the premixing zone, is imparted a swirl by a number of guide devices and is thereafter mixed with a recirculated exhaust gas. Downstream of the premixing zone, at the transition from the premixing pipe to the burnoff pipe, a turbulence ring forms, which surrounds a turbulence return-flow zone that develops at the end of the premixing zone. The initial ignition of the mixture of incoming air and fuel takes place in the turbulence ring. [0012] In a departure from the mixing of the fuel with a mixture of incoming air and recirculated exhaust gas, European Patent Disclosure EP-A 867 658 describes a method for combusting liquid fuel in which the fuel is first evaporated in recirculated exhaust gas, and only after that is the mixture of fuel and exhaust gas made turbulent with supplied fresh air to which a swirl has been imparted, and ignited. The swirl is attained by providing an annular opening, disposed around the fuel nozzle, in the blocking disk with guide faces that generate a swirl. With the guidance of the air, an underpressure is attained, by which recirculated gases are aspirated into the flame pipe. This combustion is distinguished by previously unattained, extremely low pollutant emissions values. For forming a gasification zone with oxygen-poor hot gas and for flame stabilization, a flame pipe is provided. Upstream, there are recirculation openings on the flame pipe. On the downstream end of the flame pipe, a constriction in the pipe diameter is embodied, which lends stability to the flame. [0013] A disadvantage of this and other burners is that for stabilizing the flame, a flame pipe is required. Flame pipes are very heavily stressed parts, which are worn down by use in the combustion installation. [0014] It is therefore an object of the invention to propose a combustion method and a burner head for a low-NOx burner that Allows virtually stoichiometric combustion, which assure that the burner head makes do without a flame pipe yet good stability of the flame is nevertheless achieved, and that the burner head can be used practically regardless of the given conditions of a combustion chamber or boiler chamber and can be adapted to any desired power range. [0015] This object is attained by the characteristics of independent method claim 1 and by the characteristics of independent apparatus claim 7, respectively. [0016] In the method for combusting a fuel, fuel and incoming air are delivered to a combustion chamber and ignited in the combustion chamber. The combustion takes place inside a cool and therefore blue flame and with low pollutant emissions values. The incoming air is blown into the combustion chamber in a plurality of divergent incoming air jets that are spaced apart from one another and that intersect in the chamber. As a result, in the combustion chamber, on the one hand underpressure zones are created between each two incoming air jets, and on the other, a central underpressure zone is also created centrally between the divergent incoming air jets. Oxygen-poor exhaust gases present in the combustion chamber are therefore aspirated from outside into the underpressure zones between the incoming air jets and mix with the incoming air. This delivery of recirculated gases to the flame from outside will hereinafter be called external recirculation. In addition to the external recirculation, oxygen-poor exhaust gases are aspirated axially and counter to the flow direction of the incoming air or of the mixture of incoming air and exhaust gas into the central underpressure zone. This axial delivery will hereinafter be called internal recirculation. [0017] The incoming air jets intersecting one another in the chamber also intersect a common center axis in the chamber. Because of the inclination of the incoming air jets relative to a plane that includes the common center axis and intersects the incoming air jet, the incoming air jets cause a rotation of the incoming air about the center axis. [0018] The burner head has a blocking disk, with which an incoming air conduit of a blue-flame burner can be closed off on the downstream end. In the blocking disk, there are at least two openings diametrically opposite one another, and preferably, depending on the burner power, three, four, five, six, seven, or eight openings arranged in a ring. For low power levels, optionally up to 12 openings may be provided. These openings are equipped with guide blades for guiding the air, flowing out of the incoming air conduit through the openings, in the form of incoming air jets that diverge from and intersect each other in the chamber. Between the guide blades, blocking blades are embodied, so as to achieve underpressure zones between the incoming air jets. Downstream of the blocking disk, there is a chamber in which the incoming air jets can spread apart from one another without hindrance. The guide blades and blocking blades preferably form the final air-guiding parts before the flame. As a consequence, a flame is entirely surrounded by exhaust gases present in the combustion chamber. Optionally, a short pip may be provided around the blocking disk, for metering the recirculating exhaust gases along or near the blocking disk. [0019] With this method and this apparatus, the hydrodynamic and physical-chemical preconditions have successfully been created for stable, practically stoichiometric combustion of heating oil, essentially regardless of the shape and size of the combustion chamber. The combustion produces extremely little pollution, and burners with power levels to suit heating requirements ranging from those of a single-family house to those of entire housing developments or industrial plants are feasible. Since the burner has no flame pipe, it is practically maintenance-free. In a sense, the flame floats at a distance from the blocking disk and the nozzle in the combustion chamber. The flame is cup-shaped and has very soft, frayed contours with innumerable tips that are oriented outward and inward relative to the cuplike shape. The combustion is very quiet and has almost no tendency to pulsation. The sound level values measured in the combustion of heating oil are the quietest of all, compared with those of the most commonly used yellow-flame burners and blue-flame burners. [0020] A flow axis of each incoming air jet preferably has a minimum spacing from a center axis that is common to all the incoming air jets. The spacing of the axes of the incoming air jets from the center axis is everywhere greater than zero. Thus the flow axes do not intersect the center axis. This creates a swirl effect on the gas flow in the region of the flame. This swirl serves to hold and stabilize the flame. [0021] The angle between a center axis and the divergent incoming air jets can be adjusted by the angular position of the guide blades and the angular position of the blocking blades. As a function of this angle of the incoming air jets, the cup shape of the flame is more or less widely open. Preferred half-apex angles of a cone, inscribed into the air jets and tangent to them at their entry into the combustion chamber, are between 30.degree. and 45.degree.. However, the flame stability is not threatened even at angles of 20.degree. or 60.degree.. The flow axes of the incoming air jets assume an angle to a jacket line of a cone or cylinder that touches the incoming air jet axis. Since the axes of the incoming air jets do not intersect at a common point of the center axis, the incoming air jets bring about a swirl about the center axis. The incoming air jet axes are theoretically located in a surface of rotation about the center axis that widens in the shape of the bell of a trumpet. In actuality, however, because the cross section of the cup shape of the flame increases with the distance from the blocking disk, an underpressure zone develops in the center of the flame. The effect of this is that the incoming air jets and the recycled exhaust gases, fanned out between them, form the shape not of the bell of a trumpet, but of a tulip. The incoming air jets are therefore not rectilinear but instead rotated about the center axis; depending on the angle of inclination of the incoming air jet axis relative to the aforementioned conical jacket line, they execute a rotation of from 20.degree. to 120.degree., and preferably of approximately 90.degree. about the center axis. [0022] The incoming air jets begin already spaced apart from one another and then diverge. The minimum spacing of the axes of these jets from the center axis may be located upstream of the blocking disk, at the blocking disk, or downstream of the blocking disk. The spacing between the centers of two adjacent incoming air jets in the plane of the blocking disk is advantageously approximately twice the mean diameter of the cross section of the incoming air jets. These conditions can be adjusted by means of the size of the openings in the blocking disk, the size of the blocking blades, or the inclination of the guide blades. [0023] A departure from the aforementioned ratio is possible to a limited extend. The spacing of the centers may be six times the jet diameter, or 1.5 times the jet diameter. The ratio of the cross-sectional areas of the underpressure zone and air jets can be varied between approximately 1:2 to 5:1. In no case does the ratio of the cross-sectional areas of the underpressure zone and air jets fall below a ratio of 1:3 or exceed a ratio of 8:1. From 70 to 95%, and preferably 80 to 90%, of the incoming air forms the incoming air jets. The rest of the incoming air flows into the combustion chamber, optionally centrally around a central body, such as the fuel nozzle. At high power levels, secondary air making whose volume is 10 to 20% that of the incoming air may be brought to the flame from the outside, through an annular gap in the blocking disk or around the blocking disk. In no case, however, are the incoming air jets disposed around a central incoming air jet. [0024] If the desired external recirculation is to be achieved, the dimensions of the underpressure zones appear to be significant. For a smaller outermost width of the blocking blades, a greater pressure gradient between the incoming air and the combustion chamber pressure, or a larger cross section of the underpressure zones, is necessary overall, in order to recirculate the same quantity of combustion gas. A preferred outermost width at the outermost base of trapezoidal blocking disks is at minimum 4 to 7 and at maximum 20 to 22 mm, and especially preferably 12 to 18 mm. A preferred least spacing between round openings in a blocking disk is likewise about 15 mm. A different spacing of openings and blocking blades therefore results, depending on the diameter of a blocking disk or the spacing of diametrically opposite incoming air jets. For larger diameters and higher incoming air pressures, lesser spacings between the incoming air jets are possible. Continue reading... Full patent description for Combustion method and burner head, burner comprising one such burner head, and boiler comprising one such burner head Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Combustion method and burner head, burner comprising one such burner head, and boiler comprising one such burner head patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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