A compilation was made of the composition of peat from different areas in Sweden, or which a selected But was characterized anal co-combusted with forest residue ill controlled fludized-bed agglomeration tests with extensive particle sampling, The variation in ash-forming elements in the different peat samples was large; thus, eight peat samples were selected from the compilation to represent the variation in peat composition in Sweden. These samples were characterized in terms of botanical composition, analyzed for ash-forming elements, and oxidized using a low-temperature ashing procedure, followed by characterization using scanning electron microscopy/electron-dispersive spectroscopy (SEM/EDS) and X-ray diffraction (XRD). The selected peat samples had in common the presence of Et small fraction of crystalline phases, such as quartz, microcline, albite, and calcium sulfate. The controlled fluidized-bed agglomeration tests that co-combusted forest residue with peat resulted ill a significant increase it) agglomeration temperatures compared to combusting forest residue alone. Plausible explanations for this were in increase of calcium, iron, Or aluminum in the bed particle layers and/or the reaction of potassium with clay minerals, which prevented the formation of low molting bed particle layers, The effects oil particle and deposit formation during co-combustion were reduced amounts of rule particles and all increased number of coarse particles, The mechanisms for the positive effects were a transfer and/or removal of potassium ill the gas phase to it loss reactive particular form via sorption and/or it reaction with the reactive peat ash (SiO2 and CaO), which in most cases formed larger particles (> 1 mu m) containing calcium silicon and Potassium.