| Alternate combustion type regenerative radiant tube burner apparatus -> Monitor Keywords |
|
|
  Alternate combustion type regenerative radiant tube burner apparatusUSPTO Application #: 20070054227Title: Alternate combustion type regenerative radiant tube burner apparatus Abstract: The present invention relates to an alternate combustion type regenerative radiant tube burner apparatus which comprises a circular plate positioned between a burner unit and a main combustion chamber, so that preheated secondary combustion air is fed through an opening of the circular plate to the main combustion chamber. The burner apparatus has the circular plate (10), an annular air throat (2), a cylindrical peripheral cover (30) and a heat-transfer tube (11,16). A front end portion of the peripheral cover is integrally connected with a peripheral edge portion of the circular plate so as to prevent the secondary combustion air of the air throat from leaking on a periphery of the circular plate to the air diluting chamber (3). According to the present invention, the concentration of nitrogen oxides in the combustion exhaust gas can be definitely prevented from increasing, without being affected by the installation condition or thermal deformation of the radiant tube burner apparatus. (end of abstract) Agent: Jacobson Holman Pllc - Washington, DC, US Inventors: Takeshi Tada, Susumu Mochida, Shinya Kitahara, Shinichiro Fukushima, Yutaka Suzukawa, Masaharu Suga, Isao Mori, Hitoshi Oishi, Munehiro Ishioka, Toshiaki Hasegawa USPTO Applicaton #: 20070054227 - Class: 431181000 (USPTO) Related Patent Categories: Combustion, Fuel Disperser Installed In Furnace, Plural Feed Means Extending To Common Wall Opening Of Furnace The Patent Description & Claims data below is from USPTO Patent Application 20070054227. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD OF THE INVENTION [0001] The present invention relates to an alternate combustion type of regenerative radiant tube burner apparatus, and more particularly, to such an apparatus which has a circular plate positioned between a burner unit and a combustion chamber so that preheated secondary combustion air is fed through an opening of the plate to the combustion chamber. BACKGROUND OF THE INVENTION [0002] A radiant tube burner apparatus indirectly heating an inside atmosphere of a furnace is practically in use as heating means of a heating furnace for steel, furnace for heat treatment, and so forth. As a kind of the radiant tube burner apparatus, the alternate combustion type regenerative radiant tube burner apparatus is known in the art, in which regenerators of honey-comb structures are provided on both end portions of a radiant tube (Japanese patent laid-open publications Nos. 8-247421, 11-108315, 11-108316, and U.S. patent publication No. 6,027,333). [0003] Conventionally in the alternate combustion type regenerative radiant tube burner apparatus, a velocity of injection of combustion air tends to be set at a relatively high value in order to reduce the concentration of nitrogen oxides in the combustion exhaust gas. Therefore, loss of the total pressure in the burner apparatus increases, so that a large capacity of intake blower and a large capacity of exhaust blower have to be installed in many cases. In view of such drawbacks, the present inventors have proposed an alternate combustion type regenerative radiant tube burner apparatus in Japanese patent application No. 2000-237677 (Japanese patent laid-open publication No. 2002-48334), wherein a circular plate is positioned between a burner unit and a main combustion chamber inside of a radiant tube so that fuel and primary combustion air are fed to the main combustion chamber by means of a heat-transfer tube extending through the circular plate. According to this arrangement of the burner apparatus, a distal end portion of the heat-transfer tube protrudes from the circular plate into the main combustion chamber and opens thereto. An inside space of the heat-transfer tube constitutes a primary combustion chamber for mixing the primary combustion air and the fuel. An air diluting chamber in an annular form, which opens to the main combustion chamber, is defined around the distal end portion of the heat-transfer tube. Secondary combustion air is heated up to a high temperature by heat-transfer contact with a regenerator and then, enters the air diluting chamber through an opening of the circular plate. The secondary combustion air ejected to the main combustion chamber is diluted with combustion gas of the main combustion chamber. According to the radiant tube burner apparatus thus arranged, it is possible to reduce the velocity of secondary combustion air down to 20 m/s.about.50 m/s, thereby reducing the loss of total pressure in the radiant tube burner apparatus without increasing the concentration of nitrogen oxides in the combustion exhaust gas. [0004] However, in experiments for practical use of the radiant tube burner apparatus with this arrangement, a phenomenon has taken place in which the concentration of nitrogen oxides in the combustion exhaust gas increases, depending on setting of an attitude or orientation of the radiant tube burner apparatus. It has been found that such increase in the concentration of nitrogen oxides is also caused by thermal deformation of a tube portion. [0005] The attitude or orientation of the radiant tube burner apparatus is of the nature to be appropriately changed in its design, depending on the purpose or structure of the furnace, i.e., the condition of its installation. Further, the thermal deformation of the tube portion is apt to be remarkably caused in a middle-sized or large-sized radiant tube burner apparatus with an increased diameter. Therefore, it is necessary to definitely prevent increase in the concentration of nitrogen oxides in the combustion exhaust gas due to such causes. [0006] It is an object of the present invention to provide an alternate combustion type regenerative radiant tube burner apparatus, which has the circular plate positioned between the burner unit and the main combustion chamber so that the preheated secondary combustion air is fed through the opening of the plate to the main combustion chamber, wherein the concentration of nitrogen oxides in the combustion exhaust gas can be definitely prevented from increasing, without being influenced by the installation condition or thermal deformation of the apparatus. DISCLOSURE OF THE INVENTION [0007] The present inventors have found that the concentration of nitrogen oxides in the combustion exhaust gas can be definitely prevented from increasing, by fully blocking the secondary combustion air flowing through a peripheral edge portion of the circular plate to the main combustion chamber. The present inventors have attained the object of the invention as set forth above, based on such findings. [0008] The present invention provides an alternate combustion type regenerative radiant tube burner apparatus having a radiant tube (14) defining a main combustion chamber (4) and burner units (15) provided on both end portions of the radiant tube, the burner unit being provided with a regenerator (13) and fluid passages (17, 18) for primary combustion air and fuel, the regenerator being alternately in heat-transfer contact with secondary combustion air or combustion exhaust gas, and the fluid passages extending through the regenerator, comprising: [0009] a circular plate (10) positioned between said burner unit (15) and said main combustion chamber (4); an annular air throat (2) provided between the circular plate and the regenerator, into which the secondary combustion air flows after passing through said regenerator; a cylindrical peripheral cover (30) extending from a peripheral edge portion of said circular plate to a peripheral edge portion of said regenerator; and a heat-transfer tube (16) protruding forward of said circular plate and opening to said main combustion chamber; [0010] wherein a fuel injection port (17a) and a primary combustion air delivery port (18a, 18b) open in said heat-transfer tube, an inner area of the heat-transfer tube constitutes a primary combustion chamber (1) for mixing the primary combustion air and the fuel, an annular air diluting chamber (3) opening to said main combustion chamber is formed around a distal end portion of the heat-transfer tube, and said circular plate has an opening (12) for communication between said air throat and said air diluting chamber; and [0011] wherein a front end portion of said peripheral cover is integrally connected with the peripheral edge portion of said circular plate so as to prevent the secondary combustion air of said air throat from leaking at a periphery of said circular plate to said air diluting chamber. [0012] In the radiant tube burner apparatus according to the present invention, the secondary combustion air, which has been heated up to a high temperature by heat-transfer contact with the regenerator, flows into the air throat and ejects through the opening of the circular plate to the air diluting chamber. The fuel takes a combustion reaction with the primary combustion air in the primary combustion chamber, so that the fuel is diluted with combustion gas produced by the combustion reaction. The flow of secondary combustion air, which ejects through the opening of the circular plate into the air diluting chamber, induces combustion gas of the combustion chamber, so that a combustion gas recirculation flow reverses into the air diluting chamber. This recirculation flow moves along an outer circumferential surface of the heat-transfer tube to the proximity of the opening and mixes with the flow of secondary combustion air, so that the secondary combustion air is diluted with the combustion gas. The flow of secondary combustion air having an oxygen density or air ratio reduced by mixing with the combustion gas is mixed with the mixed gas flow (F) ejecting from the primary combustion chamber (the fuel diluted with the combustion gas of the primary combustion chamber), whereby a combustion reaction between the mixed gas and the secondary combustion air generates and progresses in the main combustion chamber. [0013] In this kind of radiant tube burner apparatus, a predetermined clearance between the outer edge portion of the circular plate and a wall of the radiant tube is settled for relieving thermal stress of the circular plate and the tube wall of the radiant tube upon the thermal deformation of the tube wall. This clearance is important for incorporating the circular plate into the tube. However, when the radiant tube burner apparatus is actually equipped on a heating furnace or the like, the tube is installed in normal practice in such a position that a center axis of the tube is directed horizontally, and the circular plate is oriented vertically. Since the circular plate rests in a downward eccentric position under the influence of gravity, the clearance between the top edge of the circular plate and an inner wall surface of the tube is enlarged. In a case where the opening of the circular plate is located on a lower side, a relatively large gap or space is created between the top edge of the circular plate and the inner wall surface of the tube. Further, thermal expansion or contraction of the radiant tube and the circular plate are caused remarkably, owing to relatively significant temperature differences between a combustion operation and a pause in the combustion operation. Particularly, the thermal deformation of the radiant tube and the circular plate due to such thermal expansion or contraction appears remarkably in the middle-sized or large-sized radiant tube burner apparatus with a large diameter. This kind of thermal deformation also causes the relatively large gap or space at the peripheral edge portion of the circular plate. As the results of the aforementioned experiments conducted by the present inventors, it has been found that a relatively large quantity of secondary combustion air flow leaks through such a gap or space to the main combustion chamber, so that this flow prevents the combustion gas recirculation flow from being generated. [0014] According to the aforementioned arrangement of this invention, the air throat is defined in the peripheral cover extending from the peripheral edge portion of the circular plate to the peripheral edge portion of the regenerator, and the front edge portion of the cover is integrally connected with the peripheral edge portion of the plate to prevent the secondary combustion air from leaking to the air diluting chamber through the periphery of the plate. The combustion gas recirculation flow is not prevented from occurring, and a sufficient effect of reduction in the nitrogen oxides concentration can be obtained. Therefore, according to the present invention, the combustion gas recirculation flow can be surely generated without being affected by the installation condition or thermal deformation of the radiant tube burner apparatus, and a desired effect of reduction in the nitrogen oxides concentration can be always obtained. [0015] Further, the radiant tube burner apparatus as disclosed in Japanese patent application No. 2000-237677 has an arrangement in that the circular plate and the heat-transfer tube are supported merely in a cantilever condition by the burner unit, and the positions and attitudes of the plate and tube are apt to behave in response to the thermal deformation. However, according to the present invention, since the peripheral cover supports the circular plate in a predetermined position, the positions and attitudes of the plate and tube are stable. [0016] Furthermore, provision of the peripheral cover permits the clearance to be unintentionally enlarged, and enables intentional enlargement of the clearance or change in setting of the clearance. That is, flexibility of design in a combination of the tube and burner unit or a relative position between the tube and the burner unit can be obtained in accordance with the aforementioned arrangement of the present invention, and this enables arbitrary setting of clearance between the peripheral edge portion of the circular plate and the tube wall, setting of clearance enough to facilitate assembling or replacing works for the burner unit, standardization of design of the burner unit adaptable to differences of practical size or standard of the tube diameter and the like, or design of the burner unit applicable to different radiant tubes, and so forth. Nevertheless, the peripheral cover surely prevents the secondary combustion air from leaking through the periphery of the circular plate to the air diluting chamber, and therefore, desired effect of reduction in the nitrogen oxides concentration can be obtained by the present radiant tube burner apparatus. [0017] Preferably, the peripheral cover is contained in the radiant tube in such a condition that the thermal deformation of the cover in its axial direction is not restrained by the radiant tube and the regenerator. The relief of thermal deformation in the axial direction can prevent concentration of the thermal stress from occurring at a joint portion of the plate and the cover. That is, breakage or damage due to concentration of the thermal stress is not caused at the joint portion of the plate and the cover. [0018] The present invention also provides a radiant tube burner apparatus with the aforementioned arrangement, wherein a center (PC) of the opening (12) is positioned in a zone redially outside of a circle (R) centered on a center line (C) of the circular plate, the circle (R) having a predetermined radius S, and the radius S equals [(an inner diameter Dt of the radiant tube+ an outer diameter Dr of the heat-transfer tube)/4]. Preferably, each of the centers (PC) of the openings (12) is positioned on a center circle (PCD). The circle (PCD) has a center on a center line (C) of the radiant tube and a diameter (PCR) larger than the diameter S. More preferably, an area for positioning the opening of the circular plate is limited to a central angle range (.gamma.) equal to or less than 2500 about the center of the circular plate (.gamma..ltoreq.250.degree.). [0019] According to such an arrangement, the center (PC) of the opening (12) is eccentrically positioned on the radially outer zone of the circular plate, whereby the area for movement of the combustion gas recirculation flow is enlarged and a combustion gas inducing action of ejected flow of the secondary combustion air is enhanced. As set forth above, the secondary combustion air is prevented from leaking through the periphery of the circular plate to the air diluting chamber. In connection with this, the combustion gas of the main combustion chamber is effectively induced by the secondary combustion air flow ejected from the opening of the circular plate so that the secondary combustion air is efficiently diluted with the combustion gas in the air diluting chamber. [0020] The velocity of the airflow at the opening (12) may be set to be equal to or lower than 30 m/s, preferably equal to or lower than 25 m/s, more preferably equal to or lower than 20 m/s. Such reduction in velocity allows loss of the total pressure in the radiant tube burner apparatus to be reduced. In spite of such setting of a reduced airflow velocity, the nitrogen oxides concentration of the combustion exhaust gas can be restricted by fuel reforming (dilution) and the combustion gas recirculation, according to the radiant tube burner apparatus having the aforementioned arrangement. [0021] Preferably, a fuel injection port (17a) and a primary combustion air delivery port (18a, 18b) are positioned on a plane of the circular plate or in front thereof, and the heat-transfer tube protrudes forward from the circular plate to a relatively large extent. According to such an arrangement, a relatively large recirculation area of the combustion gas can be formed rearward of a mixture gas outlet port (a distal end portion of the heat-transfer tube). Continue reading... Full patent description for Alternate combustion type regenerative radiant tube burner apparatus Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Alternate combustion type regenerative radiant tube burner apparatus 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. Start now! - Receive info on patent apps like Alternate combustion type regenerative radiant tube burner apparatus or other areas of interest. ### Previous Patent Application: Catalytic reactor and method for the combustion of fuel-air mixtures by means of a catalytic reactor Next Patent Application: Adjustable burner Industry Class: Combustion ### FreshPatents.com Support Thank you for viewing the Alternate combustion type regenerative radiant tube burner apparatus patent info. IP-related news and info Results in 1.37296 seconds Other interesting Feshpatents.com categories: Qualcomm , Schering-Plough , Schlumberger , Seagate , Siemens , Texas Instruments , |
||
