Page 289 - Petroleum and Gas Field Processing

carbonate solution exits from the bottom of the absorbed and is flashed in

the stripper, which operates at 245 F and atmospheric pressure, where acid
gases are driven off. The lean carbonate solution is pumped back to the
absorber.
The strength of the potassium carbonate solution is limited by the
solubility of potassium bicarbonate (KHCO 3 ) in the rich stream. The high
temperature of the system increases KHCO 3 solubility, but the reaction
with CO 2 produces 2 mol of KHCO 3 per mole of K 2 CO 3 reacted. For this
reason, KHCO 3 in the rich stream limits the lean solution of K 2 CO 3
concentration to 20–35% (wt).

11.5.3 Physical Solvent Processes
Organic liquid (solvents) are used in these processes to absorb H 2 S
(usually) preferentially over CO 2 at high pressure and low temperatures.
Regeneration is carried out by releasing the pressure to the atmosphere
and sometimes in vacuum with no heat. If we apply Henry’s law,
P i ¼ HX i
or

Y i
X i ¼ P ð14Þ
H
This implies that acid gas absorbed in liquid phase (X i ) is proportional to
its gas mole fraction (Y i ) and inversely to Henry’s constant (which is
constant for a given temperature). Much more importantly, the solubility
is proportional to the total gas pressure (P). This means that at high
pressure, acid gases will dissolve in solvents, and as the pressure is
released, the solvent can be regenerated.
The properties of four of the important solvents used in natural gas
processing are given in Table 4.

Fluor Process
þ
This process uses propylene carbonate to remove CO 2 ,H 2 S, C ,COS,
2
CS 2 , and H 2 O from natural gas. Thus, in one step, the natural gas can be
sweetened and dehydrated.
Figure 8 shows a typical process flowsheet with regeneration
consisting of three flash drums. The first flash drum gas containing mostly
hydrocarbons is compressed and recycled. The second flash drum derives
expansion turbine. The third flash contains mainly acid gases. The process
is used to remove the bulk CO 2 down to 3%.

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