Slurry phase polymerisation process

Process for making a multimodal ethylene polymer in which a low molecular weight (LMVV) polymer is made in one reactor, and a high molecular weight (HMW) polymer is made in another reactor, which process comprises polymerizing in a loop reactor of a continuous tubular construction an olefin monomer optionally together with an olefin comonomer in the presence of a polymerization catalyst in a diluent to produce a slurry comprising solid particulate olefin polymer and the diluent, wherein the average internal diameter of at least 50% of the total length of the continuous tubular loop reactor is at least 700 mm and the total pressure drop in the loop of the reactor is less than 1.3 bar, the Froude number is maintained in at least one reactor of the multiple reactor system at or below 30, and the HMW polymer is produced in a reactor upstream of the LMW polymer reactor and the ratio of the average internal diameter of the HMW reactor to the average internal diameter of the LMW reactor is between 0.8 and 1.4, and further wherein the process has a polymer production rate greater than 25 tones per hour.