Fluidized bed reactor for gas phase polymerization of olefins

A fluidized bed reactor for gas phase fluidized bed polymerization of olefins, comprising:

• (I)—a first section, which is an upright cylindrical section having a diameter D1, a height H1 and a cross sectional area A1;
• and
• (II)—a frustrum shaped second section, provided vertically above the first section and centered about a common vertical axis to the upright cylindrical first section,
• (A) having a base with a cylindrical cross section of diameter D1 joined to the top of the first section, and
• (B) tapering out above its base at an angle a,
• wherein
• i) the second section has a maximum horizontal cross-sectional area A2, which is between 2.95 to 3.2 times the cross sectional area A1 of the first section;
• ii) the height H1 is between 10 to 25 m;
• iii) the angle a is between 5 to 15°;
• and
• iv) the diameter D1 is more than 4.6 m.