Page 343 - Petroleum and Gas Field Processing

Energy Separating Agent
The distillation process best illustrates a change in phase using ESA. To
separate, for example, a mixture of alcohol and water heat is applied. A
vapor phase is formed in which alcohol is more concentrated, and then
separated by condensation. This case of separation is expressed as follows:

A mixture of liquids þ Heat ! Liquid þ Vapor

For the case of NGL separation and recovery in a gas plant, removing
heat (by refrigeration) on the other hand, will allow heavier components to
condense; hence, a liquid phase is formed. This case is represented as
follows:

A mixture of hydrocarbon vapor Heat ! Liquid þ Vapor

Partial liquefaction is carried out for a specific cut, whereas total
liquefaction is done for the whole gas stream.

Mass Separating Agent
To separate NGL, a new phase is developed by using either a solid
material in contact with the gas stream (adsorption) or a liquid in contact
with the gas (absorption). These two cases are represented in the following
subsections.

13.2.2 Parameters Controlling NGL Separation
A change in phase for NGL recovery and separation always involves
control of one or more of the following three parameters:
Operating pressure, P
Operating temperature, T
System composition or concentration, x and y
To obtain the right quantities of specific NGL constituents, a control
of the relevant parameters has to be carried out:

1. For separation using ESA, pressure is maintained by direct
control. Temperature, on the other hand, is reduced by
refrigeration using one of the following techniques:
(a) Compression refrigeration
(b) Cryogenic separation; expansion across a turbine
(c) Cryogenic separation; expansion across a valve

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