ABSTRACT
Radiant tubes are used in industry for heat treatment applications in which products are treated under a protective gas atmosphere within heat treatment furnaces. Therefore the heating of such furnaces are performed with indirect fuel-red systems or electrical heating elements. For indirect red applications, the ue gas of the combustion process can not enter into the furnace. The combustion takes place within radiant tubes and the heat is transferred-via radiation-from the outer surface of the tube to the process. There are different types of radiant tubes available. For all types the maximum transferred heat is one of the important features of such systems. That means that the maximum radiant tube temperature and the temperature uniformity are important characteristics of radiant tubes. Another issue is the efciency of the radiant tubes. In
all types of radiant tubes the combustion takes place within the tube and the ue gas leaves the tube at the ue gas outlet. The efciency of radiant tubes depends on the ue gas outlet temperature. The lower the ue gas temperature the higher is the efciency of a combustion system. That means as much as possible of the provided energy must be transferred via the radiant tubes to the process and the ue gas outlet temperature must be as low as possible. One way of reducing the ue gas losses is heat recovery from the ue gas for preheating the combustion air. Therefore radiant tubes with internal air preheating technologies like plug-in recuperators, recuperative and regenerative burners have been developed.
