Process for preparing ethylene polymers in a slurry polymerization

A process for polymerizing ethylene or copolymerizing ethylene and one or more C3-C12-1-alkenes in a slurry polymerization at temperatures of from 40 to 150° C. and pressures from 0.1 to 5 MPa in the presence of a polymerization catalyst,

• wherein the process is carried out in a reactor system comprising
• a polymerization reactor configured to have a content in liquid form;
• an agitator for agitating the reactor content;
• one or more first heat exchangers located outside the polymerization reactor for cooling or heating the reactor content;
• one or more circulation pumps for withdrawing the reactor content from the polymerization reactor and circulating the reactor content through the one or more first heat exchangers;
• and
• a closed loop of a tempering medium for cooling or heating the one or more first heat exchangers, wherein the closed loop is equipped with a second heat exchangers for cooling the tempering medium and a third heat exchangers for heating the tempering medium, and
• the process comprises the steps of:
• filling the polymerization reactor with a slurry of ethylene polymer particles in a liquid medium comprising a hydrocarbon diluent;
• withdrawing slurry from the polymerization reactor;
• cooling the slurry in the one or more first heat exchangers;
• returning the cooled slurry to the polymerization reactor;
• cooling the one or more first heat exchangers with the tempering medium having a temperature in the range of from 20° C. to 50° C.;
• and
• cooling the tempering medium in the second heat exchanger by a coolant having a temperature from −20° to 45° C.