Devolatilization characteristics of coal in oxy-steam combustion were studied.
Char characteristics during devolatilization in H2O/CO2 differ from those in N2.
High concentration of H2O greatly decreases the char yields and condenses the char.
CO2 in H2O/CO2 affects char yield little but leads a less condensed char.
A relationship between the char structural features and char reactivity was set up.