Patent ID: 8034884

Claim:
A process comprising polymerizing at least one ethylenically unsaturated monomer in a gas-phase fluidized-bed reactor, the reactor comprising a single reactor chamber in the form of a vertical tube which has a region of transition in the lower section of the tube followed by a reaction zone which is followed by a calming zone in the upper section of the tube, a circulation gas line, wherein the circulation gas line is connected to the lower section of the reactor chamber, wherein the circulation gas line is directly connected to the upper section of the reaction chamber, and wherein the circulation gas line is adapted to convey a reaction gas from the calming zone to the region of transition, and a circulation gas compressor and a cooling device, the circulation gas compressor and the cooling device being sited in the circulation gas line, wherein the region of transition is adapted for transitioning the reaction gas from the circulation gas line into the reactor chamber, and wherein the region of transition is designed such that either no gas distributor plate is present or such that only a gas distributor plate is present which has a total surface area and has gas orifices, and wherein said gas orifices occupy more than 50% of the total surface area of said gas distributor plate, wherein the gas-phase fluidized-bed reactor has no internal heat exchanger in the reactor chamber, and wherein the polymerization takes place essentially in the reactor chamber and only to a minor extent parts of the polymer are circulated with the circulation gas, wherein, the reactor further comprises a closable flap situated in the region of transition from the circulation gas line into the lower section of the reactor chamber, and wherein the flap is adapted to prevent the penetration of polymer particles into the circulation gas line when the compressor is switched off.