Ash Characterization of Four Residual Wood Fuels in a 100 kWth Circulating Fluidized Bed Reactor Including the Use of Kaolin and Halloysite Additives

Abstract

Solid biomass ash related issues and adequate fuel characterization, especially for fuels with similar thermochemical properties, are still major challenges in combustion. As a consequence, the fuel switching and the valorization of unconventional available fuels are hazardous. An integrated strategy to characterize biomass fuels for ash related issues is applied to four residual woody fuels, namely, a mesquite wood mixture, rubberwood, an invader bush wood, and bamboo wood. The characterization is performed with detailed analyses including (i) ash composition, (ii) ash association forms by leaching, (iii) recently reviewed predictive correlations, (iv) thermochemical equilibrium computations to predict the ash phases formed as a function of the combustion parameters and with the use of a state-of-the-art oxide database, and (v) experimental testing in a 100 kWth circulating fluidized bed pilot reactor (CFB100). The CFB100 testing allowed investigation of the fuel ash cycle including fly ash recirculation, agglomeration and fouling tendencies, and the use of halloysite and kaolin mineral additives. Among the four fuels, bamboo evidenced the higher agglomeration trend, which increased when reducing the additive. With respect to the other fuels, rubberwood seems to have a slightly higher tendency to initiate the coating-induced agglomeration mechanism. Concerning fouling, the mesquite mixture wood is more prone to deposition, mainly because of the formation of Ca-based deposits, while for the other three fuels, ash partitioning shows that the majority of reactive alkali metals fed to the pilot is accumulated in the bottom ash and circulating material. The novel integrated strategy is successfully applied for advanced solid biomass fuel characterization for combustion.