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The fate of fuel nitrogen during the pyrolysis of brown and bituminous coals at 900 °C, in the presence of iron precipitated from FeCl3 solution, has been studied with a fluidized bed reactor. The catalysts at 0.2−0.7 wt % Fe promote N2 formation, whereas they lower nitrogen conversions to HCN, NH3, N-containing oil, tar, and char. The nitrogen distribution is not changed significantly by increasing iron loading. The effect of the iron on nitrogen distribution is larger with brown coal, the conversion to N2 being ≈50 and ≈20% for brown and bituminous coals, respectively. The size of iron particles is smaller in brown coal chars, which appears to lead to a larger catalytic effect. Comparison of nitrogen mass balances in the presence and in the absence of iron shows that N2 comes from not only volatile nitrogen but also char nitrogen. The X-ray diffraction measurements reveal the presence of graphitized carbon as well as cementite (Fe3C) in brown coal chars. These observations suggest that carbon atoms in the char substrate interact with fine particles of metallic iron and that interstitial iron nitrides formed in this process are decomposed to N2.

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Pyrolysis of five coals has been carried out at 1000−1350 °C and different heating rates with fixed-bed and free-fall reactors to examine carbon structures in devolatilized chars. The X-ray diffraction measurements show the formation of crystallized carbon with turbostratic structures, depending strongly on coal type and severity of pyrolysis. The proportion of the carbon with low rank coals decreases by demineralization with acid washing but contrarily increases by subsequent addition of Ca2+ ions, irrespective of heating rate, and a small amount of 0.5−1 wt % Ca works efficiently. It is thus likely that Ca2+ ions naturally present as ion-exchanged forms in low rank coals determine dominantly the extent of carbon crystallization at higher temperatures. The Ca added is transformed to fine particles of CaO upon pyrolysis, and a larger amount of CO is formed in the presence of the Ca. A mechanism for the Ca-enhanced carbon crystallization is discussed in terms of solid−solid interactions between CaO particles and amorphous carbon.

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