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[Zauberberg]

Regular Feed #1 to deisobutanizer column, consisting of 6m3/h n-C4 and i-C4, is coming from the upstream depropanizer column bottoms (105C, 17barg, 100% liquid). By flowing across the flow control valve (FCV), its pressure drops to 6.7barg, causing partial feed vaporization and cooling (63C, 6.7barg, 23% vapor); as such, feed enters deisobutanizer column. This is regular way of operation.

Feed #2, coming from the FCC gas plant depropanizer (6m3/h unsaturated & saturated C4s), should be routed to deisobutanizer column I mentioned, downstream of the existing FCV where flashing of regular feed occurs. There are 2 options we have to choose between:

1) To take hot C4 stream (95C, 19barg) and mix it with regular (flashed) feed. By choosing this option, combined feed has 26% vapor fraction.
2) To take the same cold C4 stream (35C, 12barg) and mix it with regular (flashed) feed. By choosing this option, combined feed is 100% liquid.

In both cases, flow of unsaturated C4s is controlled by new FCV, with minimum allowable downstream pressure of 8barg.
Column calculations showed insignificant changes in reboiler heat duty demand, overhead condensers duty and column hydraulics - almost the same in option #1 and option #2. However, option #2 is far more attractive because it eliminates column feed distributor hydraulic concerns (100% liquid feed).

I need help in following: does introducing cold C4s and having 100% liquid (combined) feed influence upstream FCV operation (line marked with red colour on the attached sketch), where flashing of regular feed takes place? In other words, will something change in this FCV operation and degree/percent of regular feed vaporization, when cold C4 stream from FCC is introduced into the common feed line - since the combined feed would consist of 100% liquid?
What other issues we need to consider when choosing between these two options?

I am attaching a simple skech of the system.
Thank you in advance, best regards.

[attachment=329:Sketch.jpg]