Knowing about the replacement necessity of fossil fuels as primary energy resource, fluidized bed combustion and gasification of biomass and anthropogenic waste feedstock have the potential to play a major role for the pursuit of this aim. The technology focuses on high thermal energy outputs (combustion) and optimal product gas yields (gasification). The bed material in fluidized bed systems, mainly used for the purpose of heat transfer and catalytic activity, has been found to interact with feedstock-derived ash. The phenomena observed and documented in literature vary from beneficial, catalytically active layer formation to disadvantageous agglomeration and defluidization. The occurrences of layer formation and agglomeration phenomena have been demonstrated to be mainly dependent on the ash composition in conjunction with bed material type. The objective of this work was the characterization of these layer formation and agglomeration processes during dual fluidized bed (DFB) steam gasification. In addition a bench-scale fluidized bed combustion (FBC) system was evaluated regarding its application as test rig for the analysis of interaction between bed material and ash. The investigated feedstocks are mainly considered waste fraction of anthropogenic use and agrarian residuals. The used feedstocks are municipal waste fraction, shredder light fraction, sugar cane bagasse, exhausted olive pomace, rice husks, and hazelnut shells. German lignite was used as feedstock additive. For benchmark and run-up operation, softwood was used. For applicability evaluation of the bench-scale fluidized bed combustion system, coniferous bark was used as feedstock. The bed material types in the DFB steam gasification operation included two different types of lime, a coarse and a fine fraction of olivine, and quartz. For the majority of DFB experiments a mixture of lime with either quartz or olivine was used. For the applicability evaluation of the bench-scale FBC system K-feldspar was applied. It proved to be a valuable test rig for the investigation of layer formation and agglomeration processes. Nevertheless, the necessity for adjustments in the feeding system and flue gas cleaning was detected. SEM and EDS analysis of different samples extracted after the processes was conducted. By means of analytical tools such as line scans and element mappings, phenomena previously mentioned in corresponding literature were detected and indicators for new phenomena are obtained. Some of the newly discovered phenomena require adjusted and focussed research. Layer formation tendency of quartz and olivine (but not lime) could be detected and compared with previous research data. The composition of quartz and olivine layers as well as the absence of alkali elements in near-surface areas of olivine are in accordance with literature data. Dominance of Si, Ca, and K in quartz particle layers and Si, Ca, and Mg in olivine particle layers was measured and quantified. The influence of SER processes on layer formation and layer stability was insufficiently detected. Agglomeration mechanisms during DFB steam gasification for quartz and olivine (but not lime) particles have been detected. The dependence of agglomeration tendencies on the produced ash fraction was detected clearly. Operation failure due to alkali-rich ash fraction, which initiated agglomeration, was investigated and driving forces determined. The ash interaction mechanisms dependent on the type of bed material have been found to be different for quartz and olivine. Neither layer formation nor agglomeration tendency could be detected quantitatively for lime bed materials. Analysis results in conjunction with ash composition data indicates, that lime bed material attrition increases the potential of Ca to interact with other bed material types.