Date of Award

Fall 11-16-2024

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

First Advisor

Yang Xiao

Abstract

The increasing generation of plastic waste and its environmental impact has driven interest in alternative disposal methods such as gasification. This study presents a techno-economic analysis of the gasification of waste plastics, specifically polypropylene (PP) and polyethylene (PE), to produce syngas. A two-stage process—thermal decomposition followed by steam reforming—was simulated using Aspen Plus. The simulation results were validated against experimental data available in the literature. The economic analysis was conducted by estimating the capital and operating costs of the gasification plant, considering factors such as feedstock costs, energy requirements, and syngas purification systems. Net Present Value Calculations were used to estimate the minimum selling price of products from the simulation. Two process configurations studies were considered. In the first configuration, PE and PP were gasified to produce syngas and later purified to obtain pure hydrogen. In the second configuration, the syngas produced was used to produce liquid fuels through Fischer Tropsch (FT) synthesis. A minimum selling price of $3.89 per kg of H2 and $1.64 per gallon was estimated for hydrogen production and the FT product stream respectively. Further, the effects of the feed composition on hydrogen yield and the minimum selling price of hydrogen were examined. It was observed that the hydrogen yield increased and consequently, the minimum selling price per kilogram of hydrogen reduced as the mass fraction of PP was increased in the feed. From the cost economic analysis, it was also observed that the cost in acquiring and preparing PE and PP based feedstock contributes significantly (80% for H2 and 70% for FT liquid fuels) to the operating cost. The equipment cost also contributes significantly to the capital cost (58% for H2 and 70% for FT liquid fuels) and the total capital investment for both configurations. A combination of sourcing cheaper feed stock and retrofitting old equipment significantly impacts the Total Capital Investment (TCI) and this could make plastic gas waste economically viable. The synthesis of syngas from waste plastics not only offers a sustainable waste management solution but also provides a potential feedstock for downstream chemical processes.

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