A model of granular flow in the regime of a moving bed under conditions of granular phase ablation is developed. The model is based on the well-known two-layer representation of stratified slurry flow, which assumes a dynamic equilibrium between the bottom (granular) layer and the upper layer of solids-liquid suspension. The mass transfer rate from the bottom layer to the upper one is defined on the basis of digestion model for a single spherical lump. The model developed allows estimation of the lengths required for the total digestion of lumps in a moving bed and the axial pressure gradient distribution for different flow regimes.