Pyrolysis of a lignite in an entrained flow reactor. 1. Effect of cations on total weight loss

Abstract

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.