Silicon carbide has the necessary strength, temperature resistance and high thermal conductivity for radiant-tube applications at high operating temperatures.
Historically, applying recuperator technology to radiant tubes usually meant placing a recuperator in the discharge of a "U" or "W" tube because straight through tubes with recuperators at the discharge end require complex hot-air return ducting at a higher installation cost. However, the development several years ago of a radiant tube within a tube eliminated the need for a separate recuperator. In this design, the gases discharging from the inner tube are returned to the inlet side by passing between the inner and outer tubes. The outer tube then receives radiation from both the inner tube and the hot return gas stream and discharges that radiation to the furnace and the load. The first burners to apply these designs were fabricated using tubes made of high-temperature alloys (Fig. 1).