A process and associated apparatus for the cooling of hot fluidized solid particles. The particles flow from a dense phase fluidized bed into the shell side of a vertically oriented shell and tube heat exchanger where cooling occurs via indirect heat exchange with a cooling media circulating in the tubes. The extent of cooling is controlled by the varying of the heat transfer coefficient between the tubes and particles in the heat exchanger which are maintained as a dense phase fluidized bed. The coefficient is varied by varying a combination of the variables comprising the quantity of fluidizing gas to the fluidized bed in the heat exchanger and the quantity of particle flow through that bed. The process has particular applicability to a combustive regeneration process and most particular applicability to the FCC process.