Process for polymerizing olefins in a fluidized bed

An olefin polymerization process comprising polymerizing at least one olefin in gas phase in a fluidized bed in the presence of an olefin polymerization catalyst in a polymerization reactor having a vertical body, a generally conical downwards tapering bottom zone, a generally cylindrical middle zone above and connected to said bottom zone, and a generally conical upwards tapering top zone above and connected to said middle zone and wherein (i) fluidization gas is introduced to the bottom zone of the reactor from where it passes upwards through the reactor;

• (ii) the fluidization gas is withdrawn from the top zone of the reactor, compressed and cooled so that a part of the fluidization gas condenses thus forming a mixture of liquid and gas, and the mixture is returned into the bottom zone of the reactor;
• (iii) a fluidized bed is formed within the reactor where the growing polymer particles are suspended in the upwards rising gas stream;
• (iv) the bed is cooled upon evaporation of the liquid;
• and (v) there is no fluidization grid in the reactor;
• characterized in that the amount of the liquid in the mixture introduced into the bottom zone of the reactor is from 0.5 to 20% by weight.