Abstract: An improved apparatus and process for treating biomass bearing material including municipal solid waste (MSW). The apparatus includes a reaction vessel configured for rotation and steam injection, with helically arranged auger vanes attached to the internal walls of the vessel, a self aligning door. Embodiments includes various of a heated jacket, modified raised projections on the top edge of the auger vanes, a modified door, modified door sealing assembly, and a process of quick charging the interior of the vessel with steam.