Combustion – Heated line section feeds flame holder – Distinct exhaust products line heats feed line
Patent
1996-05-23
2000-02-22
Price, Carl D.
Combustion
Heated line section feeds flame holder
Distinct exhaust products line heats feed line
431 11, 431 8, 431252, 432180, 432181, 432209, 126 91A, F23D 1412, F23D 1448, F23C 700
Patent
active
06027333&
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a radiant tube burner and a combustion method thereof used in industrial heating furnaces and heat treatment furnaces for heating materials.
DESCRIPTION OF THE PRIOR ART
Recently, attempts have been made to apply regenerative combustion to a radiant tube burner. Regenerative co combustion is carried out in such a manner that air for combustion is preheated with combustion exhaust gas by using a heat storage member and this preheated air is utilized for combustion. In these attempts, alternate combustion is in which burners at respective ends of the radiant burner are allowed to burn alternately and the combustion exhaust gas of one burning burner is discharged through the air throat of the other burner at pause. With the radiant tube burner of regenerative alternate combustion type, the air throat of each burner, connected to the respective heat storage member, serves as the supply passage of air for combustion and as the exhaust passage of combustion exhaust gas at the pause of combustion. Each heat storage member collects heat when a combustion waste gas passes by it and preheats air for combustion to high temperatures near the temperature of combustion waste gas with stored heat when air for combustion passes by it.
However, generally when the regenerative combustion is carried out, the preheated temperature of air for combustion reaches a high temperature, i.e., 800.degree. c. or higher and NOx increases. For this reason, suppressing the generation of NOx is considered by employing so-called two-stage combustion (U.S. Pat. Nos. 4,856,492 and 4,870,947) in which fuel is injected into the flow of air for combustion at two steps or so-called air multi-stage combustion in which air is injected into fuel at two steps to cause a combustion.
With the radiant tube burner, however, any of the above combustion schemes is difficult to execute since a fuel nozzle is generally inserted in a heat-resistant alloy radiant tube of as small caliper as 90-200 mm to form an air throat. To be concrete, with the two-stage fuel combustion scheme, though provision of a secondary fuel nozzle for injecting a secondary fuel is required downstream of the primary combustion, it is extremely difficult to have a secondary fuel nozzle provided outside or inside the primary combustion chamber in a narrow space of the radiant tube. And with the air multi-stage combustion method, to employ a double cylinder structure is indispensable to assure a passage for supplying a secondary air downstream of the primary combustion zone, but the placement thereof is extremely difficult in the radiant tube with a restricted space. Thus, the reduction principle of NOx in each of the above-mentioned combustion methods is difficult to make the best of.
Implementation of the fuel two-stage combustion method or the air multi-stage combustion method requires primary and secondary fuel supply systems or air supply systems and not only the control of them but also the structure of burners becomes complicated.
Furthermore, with a burner system in which alternate combustion is performed, fuel is left in the fuel nozzle of a not burning burner as a result of burner structure. Thus, unless the heat isolating structure of a fuel nozzle is sufficient, a problem of so-called coking is involved that the residual fuel is heated and carbonized due to a high-temperature combustion exhaust gas exhausted through an air throat.
Among various inventions made for preventing the generation of NOx, Japanese Patent Application Laid-Open No. 62-242711, for example, discloses that addition of water in a burner enables the generation of NOx to be reduced. Japanese Patent Application Laid-Open No. 63-116011 discloses that a high-load combustion based on a turning flow of primary air permits a good and stable combustion and a soft two-stage combustion in a radiant tube that enables the generation of NOx to be reduced. Japanese Patent Application Laid-Open No. 3-11202 discloses that provision of a Venturi mechanism and reci
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patent: 5479912 (1996-01-01), Dunne
Patent Abstracts of Japan of JP 62--242,711 of Oct. 1987.
Patent Abstracts of Japan of JP 63--116,011 of May 1988.
Patent Abstracts of Japan of JP 3--11,202 of Jan. 1991.
Akiyama Toshikazu
Fujii Yoshiki
Hokabori Akinori
Ishii Toshio
Kurioka Shigeo
Japan & Nippon Furnace Kogyo Kaisha, Ltd.
NKK Corporation
Price Carl D.
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