The ex-situ smoldering driven pyrolysis reactor can simultaneously remediate the organically contaminated soil/sand and valorize the plastic waste to value-added fuels. This study establishes a multidimensional model to investigate the pyrolysis of polypropylene driven by self-sustained smoldering. The melting and decomposing processes during the pyrolysis of polypropylene have been simulated using the modified apparent heat capacity method and lumped kinetic model. Using a porous structure with high thermal conductivity in the pyrolysis domain proved to be a practical approach to address the non-uniform temperature distribution and low heating rate of plastics during pyrolysis. The research focus of this study is to obtain high-quality plastic pyrolysis liquid (oil, C6–C24) within a reasonable operating time (duration of the plastic pyrolysis process). Also, the operating conditions (Darcy air velocity, initial char concentration, and PP content) determine the yield of pyrolysis products by regulating the temperature and vapor residence time. Therefore, the sensitivity analyses of pyrolysis duration and oil yield to operating conditions have been performed. It is also found that the interface wall (between smoldering and pyrolysis chambers) heat transfer coefficient determines the smoldering chamber's thermal performance. This study provides new insights into the valorization of waste plastics and the remediation of contaminated soil/sand.