When using fluidized bed in oxyfuel combustion, process parame ters must be adjusted to maintain combustion and control air leak age into the system as there are important changes in gases properties, flow, and temperature. In this sense, this work makes a description o f the retrofit o f air combustion to oxyfuel combustion in a 0.25 MWth bubbling fluidized pilot plant. Process parameters were analyzed and mass and energy balances were developed to compare air and oxyfuel combustion. Air leakage and fluidization showed to be important to control when proceeding transition to oxyfuel combustion and temperature increase was consequence o f radiation mechanism changes. I In t r o d u c t io nDifferent uses of solid fuels with the possibility of capturing CO2 have already been proposed as crucial for environmentally friendly large-scale energy generation technologies [1], Specifi cally, oxyfuel combustion consists of using oxygen instead of air in the combustion chamber and recycling part of the gases to the furnace to control the combustion temperature. Therefore, the combustion generates flue gases that are highly concentrated in C 0 2 and are supposed to be captured. Compared to air Contributed by the Advanced Energy Systems Division of ASME for publication in the Journal of E nergy Resources T echnology. Manuscript combustion, oxyfuel combustion usually affects important process parameters, which include gases recycling ratio, ignition, flame stability, heat transfer, combustion parameters, and emission kinetics [2], Moreover, two important properties changes in oxyfuel com bustion are the emissivity and heat capacity. Substituting N2 for C 0 2 at the furnace entrance increases the heat capacity. As a con sequence, a higher oxygen concentration must be used at the entrance to achieve the same flame temperature if the composition o f inert gases remains constant. Furthermore, the radiative proper ties o f C 0 2 and H20 are the opposite o f N2, thus providing higher heat transfer by radiation inside the furnace [3], According to Wail [4], higher concentrations of C 0 2 and H20 in the furnace gases result in higher gas emissivity, which signifi cantly increases the radiative heat transfer summarized the main different characteristics o f oxyfuel combustion compared to air combustion.Moreover, because recycling gases generates negative pressure, the system becomes prone to air leakage. Air leakage is a direct consequence of negative pressure in the system. Approximately, 2-4% of new plants suffer from air leakage, and this incidence increases from 8 to 16% over the plant's lifetime [5,6], Concerning the furnace technology, fluidized bed technology has already emerged as a potential and environmentally accepta ble process to generate energy by combustion [7], Upward veloc ities, i.e., when the weight o f the bed per unit of cross-sectional area exceeds the pressure drop across the bed, are a necessity of fluidized bed combustion. If upward velocities occur, the fluidiza tion velocity must be maintained below this upw...