Layer Formation on K-feldspar in Fluidized Bed Combustion and Gasification with bark and chicken manure

Abstract

The layer formation on bed materials in fluidized bed applications is an often-studied phenomenon where most work has focused on combustion but some studies on gasification exists, and direct comparisons of layer formation in combustion and gasification have been performed occasionally. The present work provides a thorough comparison of layer formation during combustion and gasification with K-feldspar as bed material using different feedstocks, namely Ca-rich bark; Ca- and P-rich chicken manure; and an admixture of chicken manure with bark. The feedstocks are tested in a 5 kW bubbling fluidized bed combustor and a 100 kWth dual fluidized bed steam gasifier. A reference bed material sample from the industrial biomass combined heat and power plant (CHP) in Senden is used as example for the gasification of bark-rich logging residues. The formed bed particle layers on the bed material surface are characterised using combined scanning electron microscopy and energy-dispersive X-ray spectroscopy; area mappings and line scans are carried out for all samples. The obtained data shows no essential influence of operational mode on the layer formation process. During the combustion and gasification of Ca-rich feedstocks a layer rich in Ca formed while K is diffusing out of the layer. The use of Ca- and P-rich feedstocks inhibited the diffusion of K and a layer rich in Ca and also P formed. The addition of P to the feedstock by chicken manure therefore changed the underlying layer formation processes.