A fluid bed reactor is configured to process a reactive material to form one or more products. The reactor includes a reaction vessel defining a compartment configured to receive the reactive material. A first cluster of heating conduits at least partially occupies the compartment and extends over a first vertical extent within the compartment. A second cluster of heating conduits partially occupies the compartment and extends over a second vertical extent within the compartment. The first cluster of heating conduits is vertically below the second cluster of heating conduits and spaced apart therefrom by a first separation distance. Feedstock inlets are configured to introduce the reactive material into a region that is vertically between the first and second clusters of heating conduits. The heating conduits in the first cluster have a first thickness while the heating conduits in the second cluster have a second thickness. The first separation distance is at least as great as the smaller of the first and second thicknesses.