Abstract: A method for adjusting and controlling the temperature in chemical reaction, that is, of cooling or heating fluidized beds wherein the fluidized bed is demixed into two or more sectional fluidized beds having different rates of longitudinal particle mixing, by dividing a flow of fluidizing gas and/or liquid into two or more flows to be supplied to different levels of the fluidized bed, the rate of cooling or heating being modified by changing the throughflow of the fluidizing gas and/or liquid within said individual flows. One or more of the sectional fluidized beds are associated with heat exchangers.