On the exergoeconomics of the thermochemical recycling of end-of-life tires by pyrolysis

This work presents the exergoeconomic assessment of a 1000 kg/h model industrial plant for the pyrolysis of end-of-life tires (ELTs) to produce raw recovered carbon black (RRCB), tire pyrolysis gas (TPG), and tire pyrolysis oil (TPO) for subsequent distillation. TPG is deemed to be used for both supplying the energy needed for pyrolysis and generating electricity through an internal combustion gas engine (ICGE). The resulting hot flue gases from the ICGE are proposed to provide the energy for the TPO distillation stage. The thermodynamic characteristics of the streams were determined based on results obtained at laboratory scale. After mass, energy, and exergy balances, the exergoeconomic principles were applied to estimate the exergy and monetary cost of the plant products. Exergy destruction in each subsystem was estimated, as well as the production costs of the TPO, its distillate fractions, the TPG, and the RRCB, among others, considering a variation of the ELTs price between −10 USD/t and 400 USD/t. An alternative approach was also evaluated in which electric heaters instead of combustion gases drive the pyrolysis and TPO distillation processes. Although technically feasible, this alternative plant could be more sensitive to heat losses which compromises its energy self-sufficiency. However, the current trend toward chemical industry electrification and the ability to precisely control pyrolysis and distillation parameters to improve product quality make this route highly attractive. These analyses aim to consolidate the advantages of scaling up the pyrolysis process and its potential to pursue the circularity of ELTs and the defossilization of the tire industry.