A dual-fluidized bed experimental apparatus was operated to study coal combustion behavior under the Calcium Looping (CaL) process temperature conditions. This apparatus consisted of a fast fluidized bed regenerator and a bubbling fluidized bed carbonator. High-volatile bituminous coal and semi-anthracite were burned in oxygen-enriched air in the regenerator. The formation of CO and CO2 in the carbonator caused by oxidation of char, which was transported from the regenerator with circulating bed material, was measured. Inert silica sand was employed as the bed material so that the produced CO2 could be measured without being captured by the bed material. The effect of the O-2 concentration in the fluidizing gas of the carbonator on the formation of CO and CO2 was evaluated. The formation rate of CO and CO2 in the carbonator was governed by different controlling factors depending on coal rank. NOx formation in the regenerator was also measured. The oxygen concentration in the carbonator fluidizing gas had only a minor influence on NOx emissions from the regenerator irrespective of char consumption in the carbonator.