Page 214 - Petroleum and Gas Field Processing

Hydrogen sulfide is normally the major sour component having
a vapor pressure greater than propane but less than ethane.
Normal stage separation will, therefore, liberate ethane and
propane from the stock tank liquid along with hydrogen sulfide.
Stripping efficiency of the system can be improved by mixing a
lean (sweet) stripping gas along with the separator liquid between
each separation stage.
Figure 6 represents typical stage vaporization with stripping
gas for crude oil sweetening/stabilization. The effectiveness of this
process depends on the pressure available at the first-stage
separator (as a driving force), well stream composition, and the
final specifications set for the sweet oil.
2. Trayed stabilization with stripping gas. In this process, a tray
stabilizer (nonreflux) with sweet gas as a stripping agent is used as
shown in Figure 7. Oil leaving a primary separator is fed to the top
tray of the column countercurrent to the stripping sweet gas. The
tower bottom is flashed in a low-pressure stripper. Sweetened
crude is sent to stock tanks, whereas vapors collected from the top
of the gas separator and the tank are normally incinerated. These
vapors cannot be vented to the atmosphere because of safety
considerations. Hydrogen sulfide is hazardous and slightly heavier
than air; it can collect in sumps or terrain depressions.
This process is more efficient than the previous one.
However, tray efficiencies cause a serious limitation on the
column height. For an efficiency of only 8%, 1 theoretical plate

Figure 6 Crude sweetening by stage vaporization with stripping gas.

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