Experiments were carried out in a pilot-scale (a0.45 m i) vortexing fluidized bed combustor (VFBC), with coal particles as the fuel, limestone as sorbent, and river sand as the fluidizing medium. The effects of various operating parameters on the combustion efficiency and the pollutants emitted were investigated. Different formulae for the combustion efficiency are compared. A combustion efficiency of 96% can be easily obtained in a VFBC. Both the NOx and SOx emissions, based on an oxygen content of 6 vol.% in the Rue gas, are found to be below 100 ppm. The retention of sulfur by limestone displays a maximum temperature in the bed at 850-880 degrees C.