Pyrolysis characteristics of metal ion-exchanged Shendong coal and its char gasification performance

Abstract

The effects of ion-exchanged metal cations (Na+, K+, Ca2+, Mg2+, Co2+ and Ni2+) on the pyrolysis reactivity of Shendong demineralized coal (SD-coal) and the gasification performance of pyrolysis chars were investigated by Py-GC/MS, TG-FTIR, FBR (the fixed-bed reactor), FTIR, SEM, XRD and CO2 reactivity. The results show that the order of pyrolysis weight loss rates is SD-coal-Ni > SD-coal-Co > SD-coal-Mg > SD-coal-Na > SD-coal-Ca > SD-coal-K. The char yields decrease and the pyrolysis gas yields increase during the pyrolysis of metal ion-exchanged coals compared with those of SD-coal. Ion exchange of Co2+ and Ni2+ increases the coal tar yields, especially the yield of coal tar obtained from SD-coal-Co pyrolysis increases to 9.45 %. Ion exchange of alkali and alkaline earth metal cations is generally conducive to the formation of naphthalene and its derivatives in coal tar. The catalytic effect of these metal cations on coal pyrolysis is Na+ > K+ > Ni2+ > Ca2+ > Mg2+ > Co2+. The values of Lc and Nave in chars derived from metal ion-exchanged coal pyrolysis are reduced compared with SD-coal char. The effect of ion-exchanged metal cations on the gasification reactivity of chars is K+ > Na+ > Mg2+ > Co2+ > Ni2+. And on this basis, the mechanisms of metal ion-exchanged coal pyrolysis and char gasification are concluded.