Thermochemical Recycling of Automotive Shredder Residue by Chemical-Looping Gasification Using the Generated Ash as Oxygen Carrier

Abstract

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.

Interactions between Automotive Shredder Residue and Olivine Bed Material during Indirect Fluidized Bed Gasification

“…Other compounds that were identified as having minor contributions to the oxygen transport were Ni, Mn, and Cu. The study of Pissot et al 7 also showed that the presence of S in the ash could further add to the oxygen carrying through cycles of CaSO 4 /CaS, as described earlier. 37 Thus, that study 7 confirmed the beneficial effects of the inherent oxygen carriers accrued from the ASR ash interaction with the bed material under CLG conditions.…”

“…The oxygen partial pressure for the oxidizing condition in the boiler was assumed to be 0.2 atm. In the gasifier, the partial pressure of oxygen was calculated to be on the order of magnitude of 1 × 10 −18 atm, given the composition of permanent gases leaving the gasifier, as reported by Pissot et al, 7 where the gas composition of the same experiment was investigated.…”

“…Pissot et al 7 studied the thermochemical recycling of ASR using CLG. Based on the results of the CLG experiments, Fe was identified as one of the main constituents of the ash and was considered most likely to be the main oxygen-carrying compound in the bed.…”

“…The material for this study originates from a CLG experiment by Pissot et al 7 where the focus has been on product gas optimization. Partial analysis of the material has previously been conducted by Stanicǐćet al 38 with the main focus on trace elements.…”

Dual Fluidized Bed Gasification Configurations for Carbon Recovery from Biomass

“…Among the existing thermochemical processes, dual fluidized bed (DFB) gasification presents a number of attractive features, including its flexibility in terms of fuel input, high heat- and mass-transfer rates, homogeneous temperature profile, and the production of raw gas not diluted with nitrogen, without the need for producing pure oxygen. DFB gasifiers have been tested at the industrial scale with biomass − and at the semi-industrial ,, and pilot , scales with plastic waste. As shown in Figure , a DFB gasifier consists of two interconnected reactors: a gasifier, in which the fuel reacts with steam to form a raw gas, and a combustor, where part of the char from the fuel is burnt to produce the heat required for the gasification reactions, with the char and heat being transported by the bed material that circulates between the two reactors.…”