Molten Solar Salt Pyrolysis of Mixed Plastic Waste: Process Simulation and Technoeconomic Evaluation

A process simulation and a technoeconomic evaluation of using molten solar salt as the heating medium for pyrolysis of mixed plastic waste (MPW) containing poly(vinyl chloride) were performed. The use of molten salt was found to be convenient for the removal of chlorine by adding calcium carbonate (CaCO3) into the salt mixture. The energy source to melt the salt was either electricity generated using the noncondensable pyrolysis gas or concentrated solar power (CSP). Mass and energy balances of the pyrolysis plant were performed using Aspen Plus simulation software. The total area of parabolic trough collectors for the solar field was calculated to supply sufficient mass flow of molten salt for the pyrolysis plant based on the mass and energy balances. Economic evaluation of the total capital investment (TCI) and return on investment (ROI) were conducted for various scenarios by varying the production scale and energy sources. When the electricity generated from the noncondensable pyrolysis gas is used as the energy source, the TCI and ROI are $3.63 million and 27.6%, respectively, for a plant scale of 8000 t/yr and $6.44 million and 49.1%, respectively, for a plant scale of 16,000 t/yr. When the energy source is CSP, the TCI increases by 20% and the ROI decreases by 11%, but the minimum selling price of the pyrolysis product oil/wax is similar because of the reduction in the production cost. The use of molten salt significantly reduces the TCI and improves the ROI when compared with the use of a conventional fluidized bed reactor. Through sensitivity analysis of the factors (TCI, main revenue, and price of MPW) affecting the net present value (NPV) of the investment, it is found that the main revenue is the most sensitive factor affecting the NPV. The results demonstrate that the molten solar salt process is a viable option for the pyrolysis of MPW and can be used either in its own right (without CSP) where solar energy is insufficient or integrated with CSP where solar energy is sufficient.