Patent ID: 8148478

Claim:
A process for the polymerization of olefins comprising polymerizing monomers in a gas-phase reactor having interconnected polymerization zones, where the growing polymer particles flow upward through a first polymerization zone (riser) under fast fluidization or transport conditions, leave said riser and enter a second polymerization zone (downcomer) through which they flow downward under the action of gravity, leave said downcomer and are reintroduced into the riser, a gas recycle stream being withdrawn from said first polymerisation zone, subjected to cooling below its dew point, thereby partially condensing the gas recycle stream to form a liquid, and then returned to said first polymerisation zone, wherein the gas recycle stream is cooled at a temperature Tc ranging from 0.5° C. to 2° C. below its dew point, wherein the liquid obtained by partial condensation of said recycle stream is separated from the gas and then introduced at two or more different points into the riser, and the gas mixture coming from said riser is partially prevented from entering said downcomer by introducing a gas and/or liquid mixture of different composition through at least one introduction line placed into said downcomer.