In this paper, a refractory-lined down flame furnace (DFF) with a kind of swirl burner installing at the top is designed and constructed to certify our previously explored fuel nitrogen transportation mechanism based on a fixed-bed reaction platform. In our previous research based on two different kinds of experiments, there are several conclusions about oxy-fuel combustion technology: (1) In oxy-fuel combustion, the preact of fuel NO release is more obvious than that in O-2/N-2 and the amount of NO released is the lowest when at the highest temperature. (2) Fuel NO is redistributed that the proportion of volatile NO is increased from 50% at 1000 degrees C to nearly 100% at 1600 degrees C for bituminous coal, and it is the same trend for lignite and anthracite. (3) The combustion characteristics of oxy-fuel are different from those in traditional conditions because the combustion duration of particles in O-2/CO2 at the temperature ranging from 1000 to 1300 degrees C is longer. On the basis of numerical simulation, the work herein is forwarded to a pilot-scale experiment applying oxidant-staged technology and the conclusions are qualitatively embedded into computational models.