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In dual fluidized bed (DFB) gasification, the interaction of the bed material with the fuel ash leads to the development of a bed catalytic activity toward tar-abating reactions. However, the formation of ash layers may also be detrimental to the process, especially in terms of the uncontrolled transport of oxygen from the combustor to the gasifier. A few previous studies investigating the development of catalytic activity in bed materials have also reported the development of oxygen transport, although the latter was not the focus of these studies. This work verifies that olivine and feldspar, which are bed materials with limited and no intrinsic oxygen transport capacities, respectively, develop the capacity to transport oxygen by interacting with the fuel ash. We correlate this development in oxygen transport to the development of bed catalytic activity. Our results imply that the volatile species that are released by the bed material to the gas phase in the gasifier contribute to the developed oxygen transport. Sulfur is proposed as one of the components of these volatile species, and its potential contribution is investigated. For feldspar, the results support the notion that sulfur is involved in the transport of oxygen, both as a volatile species and as a species remaining within the ash layer. The results also suggest that other species, including volatile ones, are involved. These aspects are investigated based on experimental results obtained from the Chalmers gasifiera semi-industrial-scale DFB gasifierand are isolated in laboratory-scale experiments.

Thermal conversion of automotive shredder residue (ASR) using indirect fluidized bed gasification was conducted in the Chalmers semi-industrial 2–4-MWth gasifier. The bed material consisted of olivine that was activated through the deposition of biomass ash prior to a 13-day exposure to ASR. The interactions between the bed material and the ASR ash were investigated using XRD, SEM-EDS, and thermodynamic modeling. The deposition of iron (Fe) onto the olivine particles was noted, and this is likely to increase the oxygen-carrying ability of the particles. Furthermore, at the end of the campaign, about one-third of the particles in the bed were found to originate from the ASR ash. These particles were rich in Fe and Si, as well as elements found exclusively in the ASR ash, such as Zn, Ti, and Cu. Some of these particles exhibited a hollow morphology, suggesting a melt state during their formation in the gasifier. In addition, a low level of agglomeration of the ash and olivine particles was detected. Thermodynamic modeling with the FactSage software indicated the formation of slag. This study presents a detailed investigation of the interactions that occur between the bed material and an ash-rich fuel such as ASR. The findings may have applications in demonstrating the induction of oxygen-carrying ability in bed materials or for metal recycling through the separation of ash particles from the bed material.