This study numerically investigates a smoldering-driven pyrolysis reactor. The reactor consists of two chambers: the smoldering chamber for the contaminated sand remediation and the pyrolysis chamber for the waste valorization. This study aims to develop a numerical model to verify the feasibility of the reactor and evaluate its thermal performance. The findings reveal that the contaminant (char) in the sand can be destroyed via smoldering and that the process can be self-sustaining after ignition. It is noteworthy that the ignition requires external energy input. Smoldering can produce a heatwave with a stable peak temperature and propagation velocity. The heatwave generated in the smoldering chamber can heat the pyrolysis chamber through the boundary. The results highlight that the reactor’s pivotal operating characteristics (peak temperature, ignition time, and reaction duration) can be regulated by the critical parameters (char concentration, air inlet velocity, and oxygen concentration).