An apparatus for pyrolyzing a carbonaceous material and producing char and volatiles includes a vessel having an inlet for the carbonaceous material, an outlet for the char and the volatiles, and a first pathway therebetween. The vessel has wall portions with interior surfaces that define the first pathway. Further, the vessel has a heat exchange medium inlet, outlet and a second pathway therebetween. The first and second pathways are in heat exchange proximity to each other and the second pathway is defined by interior surfaces of the, or other, wall interior portions of the vessel. At least some of the interior wall portions of the vessel project into an interior space of the vessel such that at least one of the first and second pathways is non-linear.