A charge gas compression train for ethylene, comprising on the same shaft line a steam turbine and a first compressor comprising a first group of compression stages , a second group of compression stages and a third group of compression stages , a. the first group of compression stages comprising an outlet configured to be connected to a first intercooler inlet , b. the second group of compression stages comprising a second compressor inlet configured to be connected to a first intercooler outlet , the second group of compression stages comprising a second compressor outlet configured to be connected to a second intercooler inlet , c. the third group of compression stages comprising a third compressor inlet configured to be connected to a second intercooler outlet , the first , the second and the third group of compression stages being integrated in a first common casing and operating at the same rotation speed of the steam turbine ; wherein the first group of compression stages , the second group of compression stages and the third group of compression stages are mounted on the same compressor shaft , the steam turbine being directly coupled with the compressor shaft , wherein the compressor shaft is formed in a single piece, or in different parts torsionally coupled to each other, characterized by the first group of compression stages comprising a plurality of unshrouded and shrouded impellers, wherein at least an unshrouded impeller is positioned upstream to at least a shrouded impeller and the unshrouded impellers have a larger diameter than the shrouded impellers , and wherein the compression train is configured to operate at a rotating speed up to 22000 rpm, preferably in a speed range comprised between 5000 and 12000 rpm. a. the first group of compression stages comprising an outlet configured to be connected to a first intercooler inlet , b. the second group of compression stages comprising a second compressor inlet configured to be connected to a first intercooler outlet , the second group of compression stages comprising a second compressor outlet configured to be connected to a second intercooler inlet , c. the third group of compression stages comprising a third compressor inlet configured to be connected to a second intercooler outlet , the first , the second and the third group of compression stages being integrated in a first common casing and operating at the same rotation speed of the steam turbine ; wherein the first group of compression stages , the second group of compression stages and the third group of compression stages are mounted on the same compressor shaft , the steam turbine being directly coupled with the compressor shaft , wherein the compressor shaft is formed in a single piece, or in different parts torsionally coupled to each other, characterized by the first group of compression stages comprising a plurality of unshrouded and shrouded impellers, wherein at least an unshrouded impeller is positioned upstream to at least a shrouded impeller and the unshrouded impellers have a larger diameter than the shrouded impellers , and wherein the compression train is configured to operate at a rotating speed up to 22000 rpm, preferably in a speed range comprised between 5000 and 12000 rpm. <EOS>