Nitrogen Release from Low Rank Coals during Rapid Pyrolysis with a Drop Tube Reactor

Nitrogen release from two low rank coals during rapid pyrolysis at 1300 °C has been studied with a graphite-made drop tube reactor, in which a graphite filter is installed for controlling a residence time of coal particles. Nitrogen distribution depends strongly on the time. At 0 s, 60−65% of coal-N is retained in the chars, and the rest is released as tar-N, HCN, NH3, and N2. When the time is prolonged to 120 s, N2 yield increases dramatically and reaches 40−55%, whereas char-N decreases mainly. There is the reverse time dependence between N2 and char-N. Demineralization with HCl washing decreases N2 but increases char-N, and the addition of 1 wt % Ca to the demineralized coal shows almost the reverse effect on N2 and char-N. The deconvolution results of C(002) XRD lines reveal that the proportion of crystallized carbon in every char increases with increasing time. The linear relationship between the proportion and N2 yield exists among all of the samples used, which strongly suggests that N2 formation from char-N occurs in the process of carbon crystallization. Such a relationship is discussed on the basis of interactions between CaO and char matrix.