Biomass as a clean and sustainable energy resource will play an important role in energy scenarios of the country in the future because of its advantages in CO2-neutral feature and considerable reduction of SO2 and NOx pollutants emitted from burning fossil fuel. Most biomass, however, is abundantly available only within a crop season, so there will be an adverse effect on stability of fuel provision, especially if it is used as a single main fuel. In order to solve this drawback, either two different biomasses or biomass and coal are blended and co-combusted. Fluidized-bed combustion (FBC) is denoted for high efficient combustion and fewer pollutants released, also, it has been proven effective when utilized for biomass combustion. This research project investigated the combustion studies performed in three different types of fluidized bed combustor: 1) a short-combustion-chamber fluidized-bed combustor (SFBC), 2) a vortexfluidized bed combustor (-FBC), and 3) a circulating fluidized bed combustor (CFBC). Both standalone combustion, and co-firing between biomass and coal were set up in SFBC and -FBC, using rice husk and bituminous coal as fuels. The combustion characteristics and performances were also taken into consideration. A study of hydrodynamics of particles inside CFBC, having been constructed, and a preliminary combustion test using wood as a fuel were also examined. The studied parameters affecting pure rice husk combustion in SFBC and/or -FBC were the fluidizing velocity, secondary air velocity, and secondary air flow fractions. The co-firing tests in SFBC and/or -FBC operated under various parameters, for examples, coal blending ratios in the range 0–25% (thermal basis), coal sizes ranging 0–5 and 5–10 mm, coal-feeding locations, as well as bed temperatures were done. The minimum fluidizing velocity (Umf), as well as pressure profiles inside CFBC operated under a variety of sizes and quantities of sand, were presented. Finally, the combustion characteristics of wood in CFBC under varying fuel feed rates were established. The results showed that in both SFBC and -FBC, the main combustion took place under the vortex ring near the fuel feed point for both cases of pure rice husk combustion and co-firing with coal. For SFBC, increased coal shares in co-firing with rice husk ameliorated the combustion efficiency (Ec), generally >98% for all coal-blending ratios. An injection of coal under the vortex ring seemed the most appropriate location in co-firing with rice husk. Meanwhile, increased shares of coal sized 5–10 mm emitted less NOx than that of 0–5 mm size. For pure rice husk firing, increases in a secondary air velocity and secondary air fractions engendered the decline of CO release and the progress in Ec, ranging 92-98%. In the cases of -FBC, increased coal shares in co-firing with rice husk were responsible for the slight decreases in Ec, and increases in SO2 and NOx emissions. High bed temperatures not only activated Ec, but also elevated SO2 and NOx as well. A higher fluidizing velocity in firing pure rice husk stimulated NOx emissions, while increased secondary air velocity lowered NOx value. The Ec for all cases were >99%. The hydrodynamics study in CFBC indicated that the increments of quantity and size of sand induced high minimum fluidizing velocity in the range of 0.18–0.46 m/s (7–9 kg-sand). The pressure profiles inside the combustor implied that solid recirculation would occur when the pressure in the Lvalve was higher than that presented in the bed. The calculated voidage along the riser was found to be in the range of 0.955–0.99. The preliminary firing test of wood in CFBC found that the combustion took place along the riser height, and increased fuel feed rates from 8 to 15 kg/h, corresponding to excess air range of 11–118%, caused the increase in temperatures inside the combustor, ranging 770–820 C.