Embodiments of a nozzle assembly and a closable valve assembly for use in a fluid bed reactor system are disclosed. The nozzle assembly includes a first member that extends upwardly through a bottom wall of a fluid bed reaction chamber, and a second member. The first and second members are detachably fitted together via threads on each member. The second member can be removed and/or replaced, thereby facilitating fluid bed reactor maintenance. The closable valve assembly is connected to a nozzle, and includes a valve body and a gate pivotally connected to the valve body. The gate is movable between a first position at least partially covering the nozzle orifice in the absence of gas flow through the orifice, and a second position wherein the orifice is not covered when gas flows through the orifice.