Screw Bed Reactor

The screw bed reactors consist of a rotating screw (Figure 7), are tubular in shape, and operate continuously. Rotation of the screw assists feedstock delivery into the reactor, while heat required for the pyrolysis process is conveyed across the tubular reactor wall. Thus, the screw serves two functions: first, mixing the feedstock and second, regulating the feedstock residence time in the reactor. A large hopper is used to feeds waste tyres into the screw bed. Inert gases are usually N2. The hopper is supplied to the hopper to eliminate oxygen from the feedstock and also make the pyrolysis system oxygen-free. By creating a modest positive pressure at the screw bed, the inert gas also aids in the transmission of pyrolysis vapour [89]. Steel and ceramic pellets are normally packed with feedstock particles, which serves as a solid heat carrier for pyrolysis. This allows feedstock particles to interact more closely as they move through the screw bed. The oil is produced by drawing the vapours produced by the pyrolysis process into a condenser. An important advantage of a screw bed reactor is that it may be made to be very compact and even portable in some situations, allowing the reactor to be used at the feedstock generating site or anywhere there is lots of feedstock. On-site feedstock processing reduces operating expenses by lowering feedstock transportation expenses to the biorefinery [90]. However, if the reactor is not designed properly, there will be poor heat transfer and temperature control, resulting in the deposition of polymeric materials in the reactor's interior [91].

**Figure 7.** Diagram of a rotary screw bed pyrolysis reactor.
