Fluidized bed combustion is a commonly used technology for a broad variety of fuels. The specific characteristics of fluidized beds (well-mixed conditions, high heat and mass transfer rates, low sensitivity toward high ash contents) are most advantageous for the treatment of difficult fuels such as high ash lignites, biomass with low ash melting point, gaseous/liquid/solid fuels with low calorific values, etc.In this contribution, a flameless stationary fluidized bed combustion (FL-SFBC) is presented. In this operational mode, all oxidation reactions are completed within the bed, while avoiding over-fire and the necessity to add secondary air above the elevated bed. Thus, the FL-SFBC allows for strict temperature control, low NOx level without subsequent flue gas cleaning, and easy dry desulfurization for high sulfur-containing fuels. In combination with a flexible decoupling of combustion heat via a steam process or a hot air turbine, the FL-SFBC serves as a decentralized power unit providing electricity and/or heat for local energy demand.Comprehensive fuel tests have been carried out in a 400 mm ID pilot scale plant. Results are presented for 2 different difficult fuels (chicken manure mixtures and catalyst-contaminated glycerine). It is shown that typical emission and bed agglomeration issues can be handled by adequate process control.