Non-catalytic ash effect on char reactivity. (15th February 2020)

• Record Type: Journal Article
• Authors: Wu, Ruochen; Beutler, Jacob; Baxter, Larry L.
• Is Part Of: Applied energy. Volume 260(2020)
• Publication Date: 2020-02-15
• Subjects: Biomass -- Gasification -- Ash -- Non-catalytic; Power (Mechanics) -- Periodicals; Energy conservation -- Periodicals; Energy conversion -- Periodicals; 621.042
• DOI: 10.1016/j.apenergy.2019.114358
• Languages: English
• ISSNs: 0306-2619

Abstract

Highlights: The mass of inert materials (ash) in a particle increases as the particle reacts. The accumulating ash fraction affects the overall particle reactivity negatively. The fuels with little ash show very little change in reactivity. The fuels with high reactivity show large changes in reactivity. The model quantitatively predicts the behavior as a function of ash content. Abstract: This investigation reviews non-catalytic ash effects on char reactivity based on several biomass chars. Biomass ash contents vary substantially among fuel types and are typified by the three fuels compared in this investigation. These fuels have ash-content ratios of about 40:1, which should allow experimental observation of ash effects. In addition, the experiments explore char gasification rates under kinetically controlled conditions that should highlight the effects of ash. By contrast, diffusion controlled burning rates may mask the types of ash effects observed here. The experimental and theoretical results indicate that refractory material such as ash reduces kinetic reaction rates by rendering portions of the surface area inert as char burnout proceeds and ash content increases. Ash also affects particle size in a somewhat compensatory manner. A theoretical model has been developed to quantify the ash effect. This model indicates that all chars from ash-forming fuels should experience similar behavior, which manifests itself as a decrease in the kinetic burning rate in late stages of burnout even though the kinetic reactivity of the char does not change.