Pyrolyzing coal blended with ash: The fate and impacts of CaSO4

Pyrolysis of Xiaolongtan lignite with and without CaSO4-containing coal ash premixed is performed at 500-850 degrees C in an infrared heating reactor to clarify the fateful roles of CaSO4 in causing effects of ash on py-rolysis. 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 degrees C. 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 4 H2 + CaSO4-* CaS + 4 H2O 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.

Automated summary

Pyrolysis of Xiaolongtan lignite with and without CaSO4-containing coal ash premixed was conducted to investigate the impact of CaSO4 on ash during pyrolysis. The presence of CaSO4-rich coal ash significantly increased the yields of CO2, pyrolysis gas, and water, while decreasing the H2 yield above 750 degrees C. Ash analysis revealed that CaSO4 mainly transformed into CaS at these temperatures, while other ash components such as Fe2O3 remained relatively unchanged. Testing the reactions between simulated pyrolytic gas and coal ash further confirmed similar decreases in H2 and CO and increases in CO2 and water, indicating that the mechanism involved the transformation of CaSO4 into CaS. Additionally, studying the reactions between char and ash showed that carbon was oxidized by CaSO4 to form CO2.