Boundary condition: x = 0, T = Tv, x = δ, T = Tb and x = −∞, T = Tu with an assumption that dT/dx is a constant throughout δ . Density of the mixture is ρ=ρairV?air+ρCH4V?CH4V?air+V?CH4+cs, and the averaged flow velocity is U=Ua·TuTa and Ua=V?air+V?CH4/πb24. Thermal conductivity is calculated based on ITMN-191 fraction, k=kairV?air+kCH4V?CH4V?air+V?CH4. The specific heat of the mixture, Ctotal=Cp+4πr3Csρsns3ρ. By integrating the Eq. (3), thickness of devolatilization zone is obtained as:equation(4)δ=k(Tb-Tν)ρUCtotal(Tb-Tu).As mentioned, when Tu is increased, Tb and U increase as well. Even though increase in Tb should contribute to increase in δ, due to corresponding increase in U, there is a net decrease in the devolatilization thickness, δ. The duration of devolatilization, or the net residence time of the mixture, is necessary to calculate total amount of extra fuel released from the coal particles. The residence time of particles is then given by:equation(5)tr=δsin(α)/U.This expression further confirms that, at a higher reactant temperature Tu, the residence time of the particle decreases due to the decrease in δ and U.