A method of producing polymer particles wherein the method comprises - polymerizing in a fluidized bed polymerization reactor comprising a fluidized bed in the reactor and the reactor having a top zone having a generally conical shape, a middle zone in direct contact with and below said top zone having a generally cylindrical shape, a bottom zone in direct contact with and below the middle zone and having a generally conical shape thereby polymerizing at least one olefin, optionally at least one comonomer and optionally hydrogen, in the presence of a polymerization catalyst and fluidization gas to obtain (i) a first stream comprising fluidization gas and particles of olefin polymer, (ii) a second stream comprising fluidization gas and agglomerates of olefin polymer, (iii) a third olefin polymer product stream, - directing the first stream comprising fluidization gas and olefin polymer particles to a series of at least three cyclones connected to the fluidized bed reactor thereby obtaining from the last cyclone in the series a final stream of fluidization gas depleted of olefin polymer particles and from the cyclones in the series a final stream of olefin polymer particles separated from the fluidization gas, - separating agglomerates of olefin polymer from the second stream comprising fluidization gas and agglomerates of olefin polymer and removing the separated agglomerates from bottom zone of the reactor, - withdrawing from the fluidized bed polymerization reactor the third olefin polymer product stream. - polymerizing in a fluidized bed polymerization reactor comprising a fluidized bed in the reactor and the reactor having a top zone having a generally conical shape, a middle zone in direct contact with and below said top zone having a generally cylindrical shape, a bottom zone in direct contact with and below the middle zone and having a generally conical shape thereby polymerizing at least one olefin, optionally at least one comonomer and optionally hydrogen, in the presence of a polymerization catalyst and fluidization gas to obtain (i) a first stream comprising fluidization gas and particles of olefin polymer, (ii) a second stream comprising fluidization gas and agglomerates of olefin polymer, (iii) a third olefin polymer product stream, (i) a first stream comprising fluidization gas and particles of olefin polymer, (ii) a second stream comprising fluidization gas and agglomerates of olefin polymer, (iii) a third olefin polymer product stream, - directing the first stream comprising fluidization gas and olefin polymer particles to a series of at least three cyclones connected to the fluidized bed reactor thereby obtaining from the last cyclone in the series a final stream of fluidization gas depleted of olefin polymer particles and from the cyclones in the series a final stream of olefin polymer particles separated from the fluidization gas, - separating agglomerates of olefin polymer from the second stream comprising fluidization gas and agglomerates of olefin polymer and removing the separated agglomerates from bottom zone of the reactor, - withdrawing from the fluidized bed polymerization reactor the third olefin polymer product stream.