Rotary Kiln Reactor

In a rotary kiln reactor shown in Figure 6, the waste tyres are fed into the front end of the reactor. The waste tyres inside the reactor are heated, moving down the cylinder, and pyrolytic gases are released. The reactor is slowly rotated and its inclined feature ensures the mixing and uniform heating of waste tyre [87]. This reactor offers various unique characteristics, such as the capacity to process heterogeneous feedstock, flexibility in residence time adjustment, proper and uniform waste tyre mixing, no need for waste tyre pre-treatment, and simple and easy maintenance. However, because of the sluggish heating rate, these reactors are mostly employed for slow pyrolysis applications. The reason for the low heating rates is that heat is transported to the feedstock from the outside reactor via the reactor wall only, and the particle size and contact area between the reactor wall surface and the feedstock are minimal. The heating rate can be achieve a maximum of 100 ◦C/min with a minimum residence time of 1 h [88]. Galvagno et al. [73] conducted an experiment on waste tyre pyrolysis in a pilot-scale rotary kiln reactor. The rotary reactor had a diameter of 0.4 m and rotated at 3 rpm, and was heated externally using 4.8 kg h−<sup>1</sup> electrical furnaces. Condensed fractions of heavy and light pyrolysis oil were condensed in a condensation system, and the non-condensable gases were cleaned to remove acid gases before being combusted in a flare. The pyrolysis char (residue) was continuously released in a water-cooled tank. They obtained 45.1% of oil, 44.3% of char, and 13.6% of gas while conducting waste tyre pyrolysis at 500 ◦C.

**Figure 6.** Diagram of a rotary kiln reactor pyrolysis reactor.
