Extraction column with alternating spillway sections

A liquid-liquid extraction column comprising the following elements:

• a first injection point (2) for injection of a first phase;
• a second injection point (3) for injection of a second phase, the first and second injection points (2, 3) being positioned on the extraction column (1) in such a way as to allow the first and second phases to circulate in the extraction column (1) in a countercurrent manner, one of the first and second phases being a continuous phase (A) and the other being a dispersed phase (B);
• a first withdrawal point for withdrawal of an extract (4) and a second withdrawal point for withdrawal of a raffinate (5), one being located at the bottom of the extraction column (1) and the other being located at the top of the extraction column (1);
• and
• a plurality of sieve trays (Pi) located from the top of the extraction column (1) to the bottom of the extraction column (1), the sieve trays (Pi) being spaced apart by an inter-tray space (8) and comprising weir plates (10) designed to hold a layer (9) of the dispersed phase (B) that has coalesced above or below the sieve trays (Pi);
• a plurality of riser/downcomer conduits (6), a riser/downcomer conduit (6) being an opening adjacent to a weir plate (10) and allowing the continuous phase (A) to pass through the sieve tray (Pi),
• the extraction column (1) comprising in alternation:
• type I sieve trays (Pi) comprising two peripheral riser/downcomer conduits (6);
• and
• type II sieve trays (Pi) comprising a single central riser/downcomer conduit (6),
• in which extraction column (1):
• the cross section S2 of central riser/downcomer conduits (6) is greater than the cross section S1 of peripheral riser/downcomer conduits (6), the cross section S1 corresponding to the sum of the cross sections of two peripheral riser/downcomer conduits (6).