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

Abstract

Interaction of biomass ash and bed materials in thermochemical conversion in fluidized beds leads to changes of the bed particle surface due to ash layer formation. Ash components present on the bed particle surface strongly depend on the ash composition of the fuel. Thus, the residual biomass used has a strong influence on the surface changes on bed particles in fluidized bed conversion processes and, therefore, on the catalytic performance of the bed material layers. Ash layer formation is associated with an increase in the catalytic activity of the bed particles in gasification and plays a key role in the operability of different biomass fuels. The catalytic activation over time was observed for K-feldspar used as the bed material with bark, chicken manure, and a mixture of bark and chicken manure as fuels. The changes on the bed material surfaces were further characterized by SEM/ EDS and BET analyses. Raman, XPS, and XRD analyses were used to characterize the crystal phases on the bed material surface. An increase in surface area over time was observed for K-feldspar during the interaction with biomass ash. Additionally, a more inhomogeneous surface composition for fuels containing chicken manure in comparison to pure bark was observed. This was due to the active participation of phosphorus from the fuel ash in the ash transformation reactions leading to their presence on the particle surface. A decreased catalytic activity was observed for the same BET surface area compared to bark combustion, caused by the different fuel ash composition of chicken manure.

Development of Oxygen Transport Properties by Olivine and Feldspar in Industrial-Scale Dual Fluidized Bed Gasification of Woody Biomass

“…The development of bed catalytic activity consequent to the formation of ash layers is manifested as an intensification of a number of reactions, including cracking and reforming reactions of tar and their precursors, − reforming of light hydrocarbons, and the WGS reaction. ,,, Since the extents of these reactions tend to increase concurrently along with the bed catalytic activity (although not necessarily having the same magnitudes), the overall catalytic activity of the bed can be represented indirectly and qualitatively using a limited number of variables. In this work, two measures of the bed catalytic activity are chosen: (1) the tar yield, expressed in g/kg daf ( i.e ., relative to the dry, ash-free fuel), which decreases with increasing bed catalytic activity in the range of temperature selected in this work; and (2) the difference in the extent of the WGS reaction relative to its equilibrium, expressed as the ratio of the quotient of reaction of the WGS reaction to its equilibrium value K WGS / K eq , which is expected to increase with catalytic activity and have a value of 1 at its maximum.…”

Early layer formation on K-feldspar during fluidized bed combustion with phosphorus-rich fuel

“…Conventionally, quartz sand is applied as bed material. Recent research attention has focused on alkali-feldspar [(K, Na)AlSi 3 O 8 ] for fluidized bed applications with biomass, to limit the problems associated with agglomeration of quartz [9,[15][16][17][18][19][20][21]. Additional to its agglomeration resistance, another advantage of feldspar is its inherent activity towards reducing the concentration of high molecular hydrocarbon species (i.e., tar).…”

“…Additional to its agglomeration resistance, another advantage of feldspar is its inherent activity towards reducing the concentration of high molecular hydrocarbon species (i.e., tar). Tar represents an unwanted side-product occurring during the related fluidized bed gasification process [16][17][18][19]. Interactions of fuel ash and bed material lead to the formation of ash layers around the bed material particles.…”

“…Interactions of fuel ash and bed material lead to the formation of ash layers around the bed material particles. These layers have been assigned different properties depending on their compositionfrom increasing the agglomeration potential of the material [22][23] to enhancing its activity towards tar reforming and gasification reactions [17][18]24]. Bed material particle layer formation was compared in a review by Kuba et al [25] for the most commonly employed bed materials, quartz, olivine, and feldspar.…”

“…The difference in exposure time limits the comparability regarding layer formation. The same samples were utilized for the analysis of the fate of phosphorus performed by Häggström et al [9] However, investigations on the catalytic activity of the same material conducted by Fürsatz et al [18] could show that the strongest increase in surface area and H 2 yield occurred within the first 8 h of the experiment.…”