Pyrolysis of plastic wastes in a fountain confined conical spouted bed reactor: Determination of stable operating conditions

The performance of both fluidized and spouted bed reactors in the pyrolysis of waste plastics is conditioned by particle agglomeration phenomena, which worsens the quality of the gas-solid contact and eventually lead to defluidization. The objective of this work is to determine the optimum conditions for stable operation (without defluidization) in a bench scale plant fitted with a fountain confined conical spouted bed reactor and equipped with a nonporous draft tube, which operates in continuous mode. The insertion of these devices enhances the gas-solid contact, especially in the fountain region, and leads to a highly stable hydrodynamic regime, with these features being of especial relevance for the in situ catalytic pyrolysis of waste plastics. This paper deals with the effect different variables have on the minimum temperature for stable operation by avoiding defluidization. The variables analyzed are as follows: plastic type (HDPE, LDPE, PP, PS, PET and PMMA), plastic feed rate, mass of inert material in the bed, spouting velocity and use of catalyst. The results show that polymers whose chains decompose at low temperatures or have high degrees of branching require low operating temperatures. Besides, as the ratio of bed mass to plastic feed rate (W-bed/Q(plastic)) and/or spouting velocity were increased, the temperature required to avoid defluidization was also reduced. The use of a catalyst also reduced the temperature required for stable operation, as the activation energy of cracking reactions is greatly reduced, and so reaction rate is increased.