Application study of pyrolysis and steam gasification of modified fly ash mixed with coal

Abstract

Coal fly ash (CF) is used in coal pyrolysis or gasification as a result of the high content of oxide metals. However, CaSO4 and SiO2 in CF inhibited catalytic activity. Herein, the application of acid-base modified CF to steam gasification of coal (CA). It was found that the order of acid-alkali modification had different effects on the H2 production. NaOH–HF (A-E) modified CF, there was no CaSO4 present on the surface of CF, and the surface SiO2 shell structure was destroyed, releasing more α-Fe and α-Fe2O3. A new Fe active phase (FexFy) had been formed. Meanwhile, the functional groups on the surface of modified CF changed, resulting in more C–H bonds, which provided more H sources for gasification. The α-Fe and α-Fe2O3 in NaOH–HF modified CF were in full contact with coal and steam, breaking the O–H bonds in the H2O, the aliphatic side-chain hydrocarbons and C–H bonds in the coal to produce more H2. α-Fe2O3 and α-Fe undergoes mutual transformation at the action of H2, providing more Fe to increasing H2 production. When the gasification temperature was 900 °C, the steam flow rate was 1 mL/min and the heating rate was 10 °C/min, the H2 yield increased from 915.97 mL/g-(E-A) to 1539.72 mL/g-(A-E), the carbon conversion of coal gasification was 99.68%.