Liquid-liquid extraction column with variable inter-tray space

Liquid-liquid extraction column (1) comprising the following elements:

• a first injection point for a first phase (2) located at an intermediate position between the top and the bottom of the column (1);
• a second injection point for a second phase (3) and a third injection point for a backwash liquid (4), one being located at the top of the column (1) and the other being located at the bottom of the column (1);
• a first withdrawal point for an extract (5) and a second withdrawal point for a raffinate (6), one being located at the bottom of the column (1) and the other being located at the top of the column (1);
• a plurality of trays (Pi) located in the column (1) and defining n zones, each zone comprising at least two trays (Pi), n being between 2 and 30;
• in which the n zones comprise:
• at least one extraction zone Zi included between a zone Z1 comprising the second injection point for the second phase (3), and a feed zone Zx comprising the first injection point for the first phase (2), x being greater than or equal to 1;
• and
• at least one backwash zone included between a zone Zx+1 and a zone Zn comprising the third injection point for the backwash liquid (4), n being greater than x;
• in which the trays (Pi) of one and the same zone exhibit one and the same height H of inter-tray space (10);
• and
• in which:
• when x is greater than 1, the height H of the inter-tray spaces (10) of the zones Zi increases when the value i increases;
• and
• when x is equal to 1, the height H of the inter-tray spaces (10) of the at least one backwash zone is less than the height H of the inter-tray spaces (10) of the zone Z1.