Cryogenic air separation (N₂/O₂/Ar)

The real Linde double-column split: air is compressed, cooled toward cryogenic temperatures, and fed to a high-pressure column; its N2-rich overhead and O2-enriched bottoms are each let down through a JT valve into a low-pressure column as two separate feeds (the HP overhead entering near the top stands in for reflux from the shared condenser-reboiler a real double column uses — this solver's column MESH doesn't expose an external reboil-duty seam, so the two columns close their own reflux independently rather than literally sharing one condenser/reboiler; everything else — two pressure-cascaded columns, real multi-feed MESH, an actual argon side column — is real). A liquid side draw near the LP column's argon pinch feeds a crude argon column that rejects oxygen (the side draw's whole point — 'crude' because a real plant needs a further deoxo + purification train for pipeline-grade argon, out of scope here).