Abstract: Polyethylene is produced in at least one reactor under a pressure of 800 to 2500 bars and a temperature of 150.degree. to 350.degree. C., and the reaction mixture exiting the reactor through an expansion valve and supplied to a separator under a pressure of 50 to 400 bars is cooled by passing a flow Q of the mixture through a turbine. The turbine comprises at least one stage with a fixed nozzle and a bladed wheel having a rotation speed of between 12,000 and 40,000 r.p.m. Ethylene discharged from the separator is recycled to the inlet of a compressor, and the discharge from the compressor is supplied to the reactor.

Abstract: Polyethylene is produced in at least one reactor under a pressure of 800 to 2500 bars and a temperature of 150.degree. to 350.degree. C., and the reaction mixture exiting the reactor through an expansion valve and supplied to a separator under a pressure of 50 to 400 bars is cooled by passing a flow Q of the mixture through a turbine. The turbine comprises at least one stage with a fixed nozzle and a bladed wheel having a rotation speed of between 12,000 and 40,000 r.p.m. Ethylene discharged from the separator is recycled to the inlet of a compressor, and the discharge from the compressor is supplied to the reactor.

Abstract: The danger of explosion due to decomposition of high-pressure industrial process gases, such as ethylene, is reduced by maintaining in an inert atmosphere at least part of an evacuation system included between a pressurized vessel within which the decomposition may take place, on the one hand, and the atmosphere, on the other.

Abstract: Process and device for cooling a mixture of polymer and monomer from a reactor in which ethylene is polymerized or copolymerized at a pressure greater than 1,000 bars between a pressure-reduction valve located downstream of the reactor and a medium pressure separator. The cooling is achieved by injecting monomer at a pressure below that of the separator using a device with a nozzle distance S.sub.1 and corresponding cross-section A.sub.1 the mixture from the reactor passes, a convergent mixing zone in which the mixture is mixed with the monomer injected, which is supplied at a flow rate q, and a diffuser of throat distance S.sub.3 and corresponding cross-section A.sub.3, which makes it possible to bring the mixture to the pressure of the separator. The dimensions of the device are such that the ratio Q/A.sub.1 is between 0.20 and 1.35 t/hr.mm.sup.2 and the ratio ##EQU1## is between 0.1 and 0.3 t/hr.mm.sup.2.

Abstract: The danger of explosion due to decomposition of high-pressure industrial process gases, such as ethylene, is reduced by maintaining in an inert atmosphere at least part of an evacuation system included between a pressurized vessel within which the decomposition may take place, on the one hand, and the atmosphere, on the other.

Abstract: Process and device for cooling a mixture of polymer and monomer from a reactor in which ethylene is polymerized or copolymerized at a pressure greater than 1,000 bars between a pressure-reduction valve located downstream of the reactor and a medium pressure separator. The cooling is achieved by injecting monomer at a pressure below that of the separator using a device with a nozzle cross-section S.sub.1 through which the mixture from the reactor passes, a convergent mixing zone in which the mixture is mixed with the monomer injected, which is supplied at a flow rate q, and a diffuser of throat cross-section S.sub.3, which makes it possible to bring the mixture to the pressure of the separator. The dimensions of the device are such that the ratio Q/S.sub.1 is between 0.20 and 1.35 t/hr.mm2 and the ratio (q+Q/S.sub.3 is between 0.1 and 0.3 t/hr.mm2.