a continuous gas fluidized bed process for the polymerization of an olefin monomer , especially ethylene , propylene , or mixtures of these with other alpha - olefins , wherein monomer - containing recycle gas employed to fluidize the bed is cooled to condense out at least some liquid hydrocarbon . the condensed liquid , which can be a monomer or an inert liquid , is separated from the recycle gas and fed directly to the fluidized bed , through a gas - induced atomizer nozzle , to produce cooling by latent heat of evaporation . the nozzle is provided with a mechanical device within the liquid inlet of the atomizing chamber , that preatomizes the liquid so that the nozzle requires reduced amounts of gas compared with conventional gas - induced atomizer nozzles .