The role of exchangeable metal cations (Ca, Mg, Na, K, Sr and Ba) in the rapid pyrolysis of a Montana lignite has been studied. The effects of variation of the cations present, and cation concentration, on weight loss and pyrolysis kinetics are presented. The reactor utilized was a dilute-phase entrained flow reactor. The reactor conditions decrease the degree of secondary reactions occurring to the primary volatile species and allow a clearer view of the fundamental pyrolysis processes. A model of the heat and momentum transfer in the reactor has been employed to estimate the particle time-temperature history. The results of pyrolysing the lignite samples display a significant role of metal cations. At 1173 K, the presence of metal cations resulted in a decrease in total weight loss at maximum residence time (0.25 s) from 50% (dry inorganic constituent free basis, dicf) for 0 wt% metal cations (acid washed) to 30% (dicf) (raw lignite, 2.8 wt% cations). Data are also presented concerning the maximum weight loss when only calcium, sodium or magnesium exchangeable cations were present. The apparent activation energy obtained from a first-order Arrhenius kinetic treatment is shown to be dependent on the presence of cations. © 1986.
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