{
  "scope": "selected physical plan/section comparison; not tray sizing or hydraulic interchangeability",
  "alternatives": [
    {
      "id": "single-pass",
      "liquid_route": "incoming edge across tray to opposite outgoing edge",
      "incoming_region": "edge downcomer hanging from above",
      "outgoing_region": "opposite-edge downcomer beginning below selected tray",
      "entry": "selected between occupied edge regions, actual elevation/approach verified"
    },
    {
      "id": "two-pass-selected-entry-level",
      "liquid_route": "incoming side regions collect toward center",
      "incoming_regions": "two side downcomers descending from above",
      "outgoing_region": "center downcomer beginning below selected tray",
      "entry": "between incoming side downcomers above outgoing-center start",
      "alternate_level": "incoming center downcomer blocks central approach; entry level differs by intervening tray in illustrated construction"
    }
  ],
  "legend": {
    "solid": "incoming/hanging physical obstruction",
    "dashed": "projected outgoing region below selected tray"
  },
  "verification": [
    "plan and section together",
    "actual opening/tray supports/internal pipes",
    "tray component passage",
    "platform/ladder/cover handling",
    "vessel/internals design"
  ],
  "numerical_permissions": null
}