A fluidized bed reactor and operating process is disclosed, the reactor including distributor plate means to provide distribution of fluid passing upwardly into a fluidized bed; mixing chamber positioned below the distributor plate neans; fluid entry means, preferably at the base of the reactor, or the passage of fluid into the reactor; flow deflector means issociated with the entry means for providing at least an up- vardly fluid flow path and an outward fluid flow path along the vall of the mixing chamber to inhibit the accumulation of solids ind liquid in the mixing chamber.