Fluidised Bed Reactor

In the oil and chemical industries, fluidised bed pyrolysis reactors are widely used. In contrast to fixed bed reactors, waste tyres in fluidised bed reactors can be processed continuously, making them very efficient and cost-effective, particularly in industrial plants [80]. This type of reactor can produce high-quality oil, with a liquid yield of 50–60% of the dry weight of the waste tyre. Waste plastics are shredded into smaller pieces and continuously fed into a pyrolyser's hot sand or other stable solid beds. To make the pyrolyser oxygen-free, the solid bed is fluidised with N2 or other inert gases. The shredded tyre quickly heated up on the solid hotbed and decomposed into vapour, char, and aerosols [81–83]. Char is removed with a cyclone separator, and the remaining vapour is quickly cooled into bio-oil and stored with a quench cooler, as shown in Figure 5. The heat required to run this type of reactor can be created by burning a portion of the produced gas in the bed or by burning char produced in another chamber and transferring the heat to the solid bed [84]. One essential feature of the fluidising bed reactor is that the shredded tyre particle sizes of less than 2–3 mm are needed to achieve the desired heating rate [85,86]. The investigations were made in this types of reactor including an industrial scale with a throughput of 200 kg h−1, a pilot scale with a throughput of 30 kg h−1, and a laboratory scale with a throughput of 1 kg h−<sup>1</sup> [65]. Williams et al. [69] pyrolysed tyre crumb (up to 1.4 mm size) in a laboratory-scale fluidised bed reactor ranging the temperature between 450 and 600 ◦C. The reactor dimensions were 100 cm in height and 7.5 cm in diameter, with a feedstock processing capacity of 220 gm kg h−1. The quartz sand was utilised as a fluidised bed, with nitrogen serving as the fluidising air, and was pre-heated to 400 ◦C using an external electrical furnace. For pyrolysis vapour condensation, a series of watercooled and dry ice/acetone-cooled condensers were used. This study found a maximum oil yield of 55% at 450 ◦C. However, the oil yield was reduced to 43.5% at 600 ◦C pyrolysis temperature and at the same time, the gas yield was increased from 2.5% to 14%.

**Figure 5.** Diagram of a fluidised bed pyrolysis reactor.
