The influence of inorganic matter on the pyrolysis of Canadian lignite in a fluidized bed

Abstract

In low rank coals much of the inorganic matter is present as cations associated with organic carboxyl groups in the coal rather than as discrete mineral phases. By treating the coal with acid the inorganic content is reduced by cation exchange, as well as by acid leaching of discrete minerals. Whole and acid treated samples of pulverized lignite were pyrolyzed in pilot scale (1 to 3 kg coal/h) and bench scale (60 to 100 g coal/h) fluidized bed reactors at atmospheric pressure, 0.45 second vapour-residence time, and temperatures ranging from 500 to 730°C. Yields of char, tar, water and light gases were determined. Removal of inorganic matter from a Saskatchewan lignite resulted in increased yields of tar and total volatile matter, with little effect on the yields of light gases. Increased yields of tar are largely a result of an increased asphaltene fraction in general and specifically of an increased catechol content. Char from acid-washed coal is less reactive to carbon dioxide than is char obtained from raw lignite.