Mathematical model for mass and heat transfer in multilevel reactor for pyrolysis of used tyres

A new vertical pyrolysis reactor with multiple hollow discs was developed to pyrolyse waste tyres into carbon black, liquid oil and fuel gas. Based on the assumptions of an annular - granular heap, a constant angle of repose and uniform physical properties, a mathematical model for the mass transfer in a multilevel reactor is presented, which provided formulae for several important parameters, such as height, volume of each granular heap, retention time and effective covering ratio. According to the penetration model of particle heat transfer and the kinetic model of tyre pyrolysis, the exit temperature T-out and rubber remnant content X-out in granular heaps were effectively predicted by a straightforward stepwise calculation procedure, and the maximum pyrolytic capacity was calculated as well. The model and equations were applied in a pilot scale system ( 3000 ta(-1)). In the results, the theoretical predictions of maximum pyrolytic capacity and exit temperature are shown to be in satisfactory agreement with the test data. The heat mass transfer model provides a theoretical basis for the optimal design of vertical pyrolysis reactor with multiple hollow discs.