A distillation column shows poor separation despite adequate reflux. What are the possible causes and how would you troubleshoot?

Poor separation causes include: damaged or misaligned trays (perform gamma scan to check tray condition), fouled trays/packing reducing efficiency (measure pressure drop across sections), poor liquid distribution (inspect distributors), incorrect feed location (verify against design), entrainment (check approach to flood), weeping at low loads (verify minimum vapor rate), or feed composition different from design. Troubleshooting: measure temperature profile, sample at multiple points, perform pressure drop survey, and consider gamma scanning for internal inspection.