Page 363 - Petroleum and Gas Field Processing

are condensed to produce reflux and liquid product. On the
other hand, for columns employing partial condensers, such as
deethanizers, product is produced as vapor (ethane).
2. Bottom reboiler temperature, which sets the amount of light
hydrocarbons in the bottom product. Adjusting the heat input to
the reboiler controls this.
3. Tower operating pressure, which is fixed by the type of
condensing medium (i.e., its temperature). Product quality is
not affected, to a great extent, by changing the operating
pressure.

13.4 SYNTHESIS OF SEPARATION (DISTILLATION)
SEQUENCES

In the separation and the recovery of NGL constituents from a gas stream,
it is required to find the optimal arrangement of the separation steps that
will be both economically and technically feasible.
In this regard, solutions are reached through some rules or heuristics
as explained next [4].

13.4.1 Cost of Separation (Fractionation)
The cost of fractionation is influenced by the following:
1. The quantity or feed input to be processed, load (L)
2. The boiling point difference between two components (Z),
defined also as the property difference between the two species
on each side of the separation breaking point
One can simply relate the cost of separation to these two variables by the
following relationship: cost of separation is a function of L/Z,or

L

Cost of separation ¼ k
Z
Because Z is fixed for a given mixture, our main objective is to select an
optimal arrangement of separation sequence that will minimize L, thus,
the cost of separation.

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.