Recycling of the carbon atoms from plastic waste is a crucial step in establishing a circular economy. The intense sorting required to produce easily treatable streams inevitably produces highly heterogeneous waste byproducts, which are challenging to recycle. In this paper, we propose that automotive shredder residue (ASR), which is one such heterogeneous waste, can be recycled by chemical-looping gasification (CLG), using its own ash as the oxygen-carrying bed material. We investigate two critical issues regarding the feasibility of the process: how to achieve complete conversion of the ASR in the fuel reactor and whether the heat of oxidation of the bed material is sufficient to fulfill the energy demand of the process, especially when complete conversion of ASR is achieved in the fuel reactor. This work is based on experiments conducted in the 2−4 MW th Chalmers dual fluidized bed gasifier. Assessed were the impacts on ASR conversion of four operational parameters: the bed material circulation rate; the ASR feeding rate; the levels of oxygen transport between the reactors; and the fuel reactor temperature. A heat balance for the system was established to assess the feasibility of CLG from the energy standpoint. The transport of oxygen was found to be the decisive parameter in the process, as it had the strongest impact on ASR conversion and directly affected the heat release in the air reactor. The oxygen transport level was found to be insufficient to cover the heat demand of the CLG process, indicating that strategies to increase oxygen transport are needed. However, carbon dioxide was found to be the main product of the process (on a carbon basis) and the carbon that was converted by increasing the oxygen transport formed carbon dioxide exclusively. Therefore, the viability of the CLG process for ASR recycling requires the valorization of carbon dioxide.
A dual fluidized bed (DFB) gasification process is proposed to produce sustainable reducing gas for the direct reduction (DR) of iron ore. This novel steelmaking route is compared with the established process for DR, which is based on natural gas, and with the emerging DR technology using electrolysis-generated hydrogen as the reducing gas. The DFB-DR route is found to produce reducing gas that meets the requirement of the DR reactor, based on existing MIDREX plants, and which is produced with an energetic efficiency comparable with the natural gas route. The DFB-DR path is the only route considered that allows negative CO2 emissions, enabling a 145% decrease in emissions relative to the traditional blast furnace–basic oxygen furnace (BF–BOF) route. A reducing gas cost between 45–60 EUR/MWh is obtained, which makes it competitive with the hydrogen route, but not the natural gas route. The cost estimation for liquid steel production shows that, in Sweden, the DFB-DR route cannot compete with the natural gas and BF–BOF routes without a cost associated with carbon emissions and a revenue attributed to negative emissions. When the cost and revenue are set as equal, the DFB-DR route becomes the most competitive for a carbon price >60 EUR/tCO2.
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