Techno-Economic Feasibility and Flowsheet Synthesis of Scrap Tire/Plastic Waste Liquefaction

A techno-economic feasibility study was undertaken to assess the viability of co-liquefying scrap tires and post-consumer plastic wastes into liquid transportation fuels. First, a generalized process flowsheet was synthesized. Next, material and energy balances as well as process simulations were developed. Finally, a profitability analysis was completed for all process scenarios investigated. Two different base case scenarios were considered: (1) the melting/depolymerization of waste plastics and the pyrolysis of scrap tires and (2) the pyrolysis of both waste plastics and scrap tires. For the techno-economic assessment, waste plastic and scrap tire feed rates of 200 and 100 tons per day respectively were assumed. Costs for individual pieces of equipment were either rigorously calculated or scaled down from literature sources. In addition to the two base case scenarios, two separate modules were also considered: (1) the melting/depolymerization and upgrading of waste plastics alone and (2) the pyrolysis and upgrading of scrap tires alone. The economies of scale for these two modules were also analyzed. The results for both base case scenarios indicate that a 15% rate of return on investment (ROI) can be achieved if a waste plastic tipping fee of $35-$45 per ton can be secured. Furthermore, the economic analysis of the two modules reveals that tire pyrolysis has an ROI of 18% while the ROI of plastic melting/depolymerization is much lower. This result is expected since the potential tips and revenues from scrap tires is greater than those from waste plastics. Due to economy of scale, the process economics for both modules is considerably improved as capacity is increased. Thus, these results affirm that the co-liquefaction of waste plastics and scrap tires as well as the liquefaction of scrap tires alone is both technically and economically feasible.