Pyrolyzing Coal Blended with Ash: The Fate and Impacts of Caso4

Abstract

Pyrolysis of Xiaolongtan lignite with and without CaSO4-containing coal ash premixed is performed at 500–850 oC in an infrared heating reactor to clarify the fateful role of CaSO4 in causing effect of ash on pyrolysis. The presence of coal ash rich in CaSO4 significantly raises the yields of CO2, pyrolysis gas and water but decreases the H2 yield at temperatures above 750 oC. Analysis of the ash after pyrolysis clarifies that CaSO4 is mainly reduced to CaS at those temperatures, and other ash components such as Fe2O3 change little. Similar decreases in H2 and CO and increases in CO2 and water are also identified in testing the reactions between simulating pyrolytic gas and coal ash, and the mechanism is thought to be 4H2 + CaSO4 → CaS + 4H2O and 4CO+ CaSO4 → CaS + 4CO2. Studying the reactions between char and ash further elucidates that carbon is oxidized by CaSO4 to form CO2 through C + CaSO4 → CaS + 2CO2.

Keywords: Coal pyrolysis, Ash, CaSO4, Gas-solid reactions, Solid-solid reactions