Abstract
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.
Highlights
Dual fluidized bed (DFB) gasification is a promising technology for the production of synthetic gas, which is a precursor to a wide range of chemicals and fuels
Additional work is needed to confirm the role of sulfur and, more generally, the roles of volatile species in the development of oxygen transport, the present study clearly shows that oxygen transport does develop along with catalytic activity in the cases of both olivine and feldspar
The present work verifies that, along with the known development of a catalytic activity by interaction with the fuel ash during DFB gasification of woody biomass, bed materials can develop an oxygen transport capability, a phenomenon previously reported in a few studies but which had not been investigated
Summary
Dual fluidized bed (DFB) gasification is a promising technology for the production of synthetic gas, which is a precursor to a wide range of chemicals and fuels. In a DFB system, the fuel decomposition reactions in the gasification reactor lead to the production of char. Part of the char exits the reactor and is transported to the combustor, where it is combusted. The heat released during the combustion is transported from the combustor to the gasifier by means of a bed material that circulates between the two fluidized bed reactors. The bed material interacts with the released gas species. Among these gas species are heavy hydrocarbons, referred to as “tar,” the presence of which in the gas can lead to operational problems. The interaction of the bed material with the gas species often results in a decrease in the tar content of the gas, a capability of the bed material that is referred to as “catalytic activity.” The use of an in-bed catalyst has been extensively investigated as a primary measure for tar abatement.[1,2] The bed material, plays a central role in DFB gasification, affecting the energy balance of the process and its product output
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