There is a significant difference between adding liqu id onto a stage and adding vapor onto the same stage. Liquid is the danse phase, and if we went to add it to stage F than the feed nozzle must be above stage F to allow the feed to fall onto the stage. Vapor
is the low density stream: if we went to add vapor to the column onto the stage. F we should place the feed stream nozzle below stage F so the feed may rise up to the stage. If the feed is two phase, the optimum conceptual design would be to make two feed nozzles, one for the vapor part of the two-phase mixture below the stage, and on for the liquid part of the two-phase mixture above the stage. This design is often not used because of the reduced convenience of the mechanical design. The three types of feed location are shown in Figure 3.24.