panels 28 a 28 b between legs 30 a 30 b and above panels 28 a 28 b the top of panels 28 a 28 b having no contact with enclosure 10 a first heat exchanger 32 is held between panels 28 a 28 b above load 14 a second heat exchanger 34 is held between panels 28 a 28 b above load 14 exchangers 32 34 are schematically shown as rectangles in fig1 and 2 in operation the quenching gas is cooled by flowing through heat exchangers 32 34 as an example each heat exchanger 32 34 comprises parallel tubes having a cooling liquid flowing therethrough quenching cell 5 comprises a planar horizontal separation plate 36 a 36 b for each impeller 22 a 22 b the median plane of separation plates 36 a 36 b contains axes u03b4 a and u03b4 b each plate 36 a 36 b connects enclosure 10 to the associated vertical panel 28 a 28 b substantially along the entire length of enclosure 10 along axis d each plate 36 a 36 b comprises an opening only opening 39 a being shown in fig4 and 6 especially providing a passage for impeller 22 a 22 b and drive shaft 26 a 26 b each plate.