화학공학소재연구정보센터
Fuel, Vol.76, No.14, 1361-1367, 1997
Effect of alkali and alkaline earth metals on nitrogen release during temperature programmed pyrolysis of coal
Formation of HCN, NH3, and N-2 during fixed-bed pyrolysis at 10K min(-1) has been studied using coal samples after partial demineralization followed by addition of metal hydroxides from aqueous systems. Without additives, NH3 is the predominant product at less than or equal to 700 degrees C, showing the two peaks in the formation rate profile, whereas N-2 is the only product at greater than or equal to 800 degrees C. The presence of NaOH, KOH and Ca(OH)(2) promotes considerable NH3 formation between 450 and 600 degrees C, but in contrast suppresses HCN formation in this region. The Ca shows the largest effect on both the promotion and suppression. It is likely that the NH3 increased by Ca addition arises partly from HCN, but mainly from secondary reactions of tar-N. These hydroxides affect N-2 formation in quite different manners: the Na decreases the rate between 700 and 950 degrees C, and the K changes it less significantly than the Na, but the Ca remarkably increases the rate in a low temperature region of 550-700 degrees C. These different features are discussed in terms of solid-phase reactions of alkali metal carbonates with char-N and secondary decomposition reactions of tar-N on CaO particles. As a result, total conversion of coal-N to HCN, NH3 and Nz up to 1000 degrees C increases in the sequence of Na < none < K < Ca.