PC. High PC concentrations mean higher carrying capacity of acid gases in the
system. Hence, these processes operate at somewhat elevated temperatures.
The system is ideal for streams having CO 2 partial pressures of 30–90 psi
(205–620 kPa). It has a high affinity for H 2 S so that pipeline specification for
H 2 S can easily be reached at about 4 ppm. A stream with little or no CO 2 is not
suited for the process due to making regeneration of the lean PC extremely difficult.
This process is often found as part of the hydrogen plant in those refineries that
need to produce hydrogen.
Sulfinol
This is a proprietary system developed by Shell Oil Company. The process uses a
solution containing both a chemically reactive component, diisopropanolamine
(DIPA), and a physical solvent, tetrahydrothiophene 1–1 dioxide (Sulfolane).
Sulfolane is a very active solvent for H 2 S, COS, and the mercaptans. CO 2 is also
soluble in it, but not nearly as much as the S compounds are. Because of this,
Sulfinol systems are most economically attractive (compared to amine systems) for
H 2 S/CO 2 ratios greater than 1:1. If the bulk of the acid gas can be dissolved in the
Sulfolane, the system is much cheaper to operate than amine. The acid gases are
picked up and released with very little heat increase or heat required. The solubility
of acid gases is much higher in Sulfinol than for the amines. Sulfinol loadings are
limited to 4–6 scf acid gas/gal solvent versus 2.5 scf acid gas/gal amine solution. In
addition, the heat capacity of Sulfolane is about half that of the amines, further
reducing the regeneration heat required.
Miscellaneous Processes
Other sweetening liquid processes such as Vetrocoke, Stretford, and Rectisol have
found high usage in the coal gasification and natural gas industries. They have not
reached the prominence of the amines or the PC processes in oil refining. Table 1
summarizes a comparison of the common solvents.
Calculating the Amine Circulation Rate
The circulation rate for amine solvents is important to ensure effective treatment of
the sour gas. It is important also because it is a major contribution to the operating
costs of the plant. These costs include pumping costs and steam to the reboiler and
air cooler/condenser costs. This section provides a calculation method to establish
this circulating rate. It is based on some fixed parameters which have been accepted
as the optimum. These steps are:
Step 1. In DEA and MEA treating processes, a ratio of the amine to H 2 S is about 3:1
mole-mole.
Step 2. Obtain gas feed rate and its composition (from plant and lab tests).
Determine its mole weight and the volume percent H 2 S.
Refinery Gas Treating Processes
507
system. Hence, these processes operate at somewhat elevated temperatures.
The system is ideal for streams having CO 2 partial pressures of 30–90 psi
(205–620 kPa). It has a high affinity for H 2 S so that pipeline specification for
H 2 S can easily be reached at about 4 ppm. A stream with little or no CO 2 is not
suited for the process due to making regeneration of the lean PC extremely difficult.
This process is often found as part of the hydrogen plant in those refineries that
need to produce hydrogen.
Sulfinol
This is a proprietary system developed by Shell Oil Company. The process uses a
solution containing both a chemically reactive component, diisopropanolamine
(DIPA), and a physical solvent, tetrahydrothiophene 1–1 dioxide (Sulfolane).
Sulfolane is a very active solvent for H 2 S, COS, and the mercaptans. CO 2 is also
soluble in it, but not nearly as much as the S compounds are. Because of this,
Sulfinol systems are most economically attractive (compared to amine systems) for
H 2 S/CO 2 ratios greater than 1:1. If the bulk of the acid gas can be dissolved in the
Sulfolane, the system is much cheaper to operate than amine. The acid gases are
picked up and released with very little heat increase or heat required. The solubility
of acid gases is much higher in Sulfinol than for the amines. Sulfinol loadings are
limited to 4–6 scf acid gas/gal solvent versus 2.5 scf acid gas/gal amine solution. In
addition, the heat capacity of Sulfolane is about half that of the amines, further
reducing the regeneration heat required.
Miscellaneous Processes
Other sweetening liquid processes such as Vetrocoke, Stretford, and Rectisol have
found high usage in the coal gasification and natural gas industries. They have not
reached the prominence of the amines or the PC processes in oil refining. Table 1
summarizes a comparison of the common solvents.
Calculating the Amine Circulation Rate
The circulation rate for amine solvents is important to ensure effective treatment of
the sour gas. It is important also because it is a major contribution to the operating
costs of the plant. These costs include pumping costs and steam to the reboiler and
air cooler/condenser costs. This section provides a calculation method to establish
this circulating rate. It is based on some fixed parameters which have been accepted
as the optimum. These steps are:
Step 1. In DEA and MEA treating processes, a ratio of the amine to H 2 S is about 3:1
mole-mole.
Step 2. Obtain gas feed rate and its composition (from plant and lab tests).
Determine its mole weight and the volume percent H 2 S.
Refinery Gas Treating Processes
507