Layer formation mechanism of K-feldspar in bubbling fluidized bed combustion of phosphorus-lean and phosphorus-rich residual biomass

Abstract

Layer formation mechanism of K-feldspar in bubbling fluidized bed combustion of phosphorus-lean and phosphorus-rich residual biomass, Applied Energy. 248 (2019) 545-554.

Impact of residual fuel ash layers on the catalytic activation of K-feldspar regarding the water–gas shift reaction

“…Figure 1 depicts the elemental composition of the fuel ash, produced at 550°C, measured by XRD, as well as the fuel ash content. A detailed overview of the experimental parameters as well as sampling conditions for the bed material samples was given by Wagner et al [17].…”

“…A detailed assessment of the ash transformation reactions in thermochemical conversion of biomass was published by Boström et al [13]. This ash layer formation has been studied for different types of bed materials, such as olivine [14], quartz [15], and K-feldspar [16,17], describing the mechanisms underlying the formation of those layers. The mechanisms differentiate significantly from another in the initiating steps of the layer formation.…”

“…Outer layers are developed by fuel ash directly accumulating on the surface so the composition of the outer layers mainly correlates with the ash composition of the fuel [18,19]. Most of the available literature is focused on phosphorus-lean fuels, but studies focusing on phosphorus-rich fuels have shown that the inner layer formation is highly influenced by the presence of phosphorus [17,20]. Layer-initiating elements like potassium and calcium normally react with silicone in the bed material, but when phosphorus is available, they will react with phosphorus instead, since it is more reactive [13].…”

“…Different residual biomasses cannot be compared easily since their composition and fuel characteristics vary greatly. Biomass ash can range from silicone-rich (e.g., straw) and calcium-rich (e.g., bark) to containing considerable amounts of phosphorus (e.g., manures) [17]. The consequences of using residual biomass, regarding the surface composition of the ash-layered bed particles and the subsequent influence on the catalytic activation, have been studied occasionally [24,25].…”

“…While studies referring to industrial-scale plants mainly focused on olivine as a bed material [26], several alternative bed materials have been studied in lab-to pilot-scale experiments, where an activation could be observed [16,17,27,28]. Studies have shown that the layer formation during (steam) gasification is comparable to layer formation during combustion [29,30].…”