Keywords
Refinery • Gas Treating • Amine • Absorber • Stripper • Sulfur • H2S
Introduction
Refinery gas treating is the generic term for processes used to remove the so called
“acid gases,” which are hydrogen sulfide and carbon dioxide, from the refinery gas
streams. The acid gas removal processes used in the refinery are required either to
purify a gas stream for further use in a process or for environmental reasons. Clean Air
legislation now being practiced through most industrial countries requires the removal
of these acid gases to very low concentrations in all gaseous effluents to the atmosphere. Hydrogen sulfide combines with the atmosphere to form very dilute sulfuric
acid and carbon dioxide to form carbonic acid, both of which are considered injurious
to personal health or may have other environmental impacts (greenhouse gases).
These compounds also cause excessive corrosion to metals and metallic objects.
This chapter describes the processes, their chemistry, and a method of calculating the design of the more common processes.
The Process Development and Description
The use of chemically “basic” liquids to react with the acidic gases was developed
in 1930. The chemical used initially was triethanolamine (TEA). However, as
monoethanolamine (MEA) became commercially more available, it became the
preferred liquid reactant due to its high acid gas absorption on a unit basis. The
molecular weight of MEA is 61, while that for TEA is 149. As both react mole for
mole with the acid gases, 2.44 lb of TEA must be circulated to achieve the same
absorptive capacity as 1 lb of MEA. TEA also suffers degradation at temperatures
above its boiling point; and, as this is its regeneration temperature, MEA has
replaced TEA in this service. Since 1955 numerous alternative processes to MEA
have been developed. These have fewer corrosion problems and are to a large extent
more energy efficient. Inhibitor systems have, however, been developed which have
eliminated much of the MEA corrosion problems. Some of these newer processes
also are designed to selectively remove the H 2 S, leaving the CO 2 to remain in the
gas stream.
The process flow and description of the more common processes are essentially
the same. This process flow is shown in Fig. 1.
For product gas streams which must meet lower than 1 grain per scf (standard
cubic foot) of H 2 S ($4.2 vol ppm), MEA (or caustic absorption) must be used. This
amine, however, is degraded by certain sulfide compounds found in gas from
thermal crackers. The most common compound that degrades MEA is carbonyl
sulfide (COS). MEA can, however, be regenerated by batch or continuous vaporization and disposal of the sludge formed by the degradation.
500
D.S.J. Jones and S.A. Treese
Refinery • Gas Treating • Amine • Absorber • Stripper • Sulfur • H2S
Introduction
Refinery gas treating is the generic term for processes used to remove the so called
“acid gases,” which are hydrogen sulfide and carbon dioxide, from the refinery gas
streams. The acid gas removal processes used in the refinery are required either to
purify a gas stream for further use in a process or for environmental reasons. Clean Air
legislation now being practiced through most industrial countries requires the removal
of these acid gases to very low concentrations in all gaseous effluents to the atmosphere. Hydrogen sulfide combines with the atmosphere to form very dilute sulfuric
acid and carbon dioxide to form carbonic acid, both of which are considered injurious
to personal health or may have other environmental impacts (greenhouse gases).
These compounds also cause excessive corrosion to metals and metallic objects.
This chapter describes the processes, their chemistry, and a method of calculating the design of the more common processes.
The Process Development and Description
The use of chemically “basic” liquids to react with the acidic gases was developed
in 1930. The chemical used initially was triethanolamine (TEA). However, as
monoethanolamine (MEA) became commercially more available, it became the
preferred liquid reactant due to its high acid gas absorption on a unit basis. The
molecular weight of MEA is 61, while that for TEA is 149. As both react mole for
mole with the acid gases, 2.44 lb of TEA must be circulated to achieve the same
absorptive capacity as 1 lb of MEA. TEA also suffers degradation at temperatures
above its boiling point; and, as this is its regeneration temperature, MEA has
replaced TEA in this service. Since 1955 numerous alternative processes to MEA
have been developed. These have fewer corrosion problems and are to a large extent
more energy efficient. Inhibitor systems have, however, been developed which have
eliminated much of the MEA corrosion problems. Some of these newer processes
also are designed to selectively remove the H 2 S, leaving the CO 2 to remain in the
gas stream.
The process flow and description of the more common processes are essentially
the same. This process flow is shown in Fig. 1.
For product gas streams which must meet lower than 1 grain per scf (standard
cubic foot) of H 2 S ($4.2 vol ppm), MEA (or caustic absorption) must be used. This
amine, however, is degraded by certain sulfide compounds found in gas from
thermal crackers. The most common compound that degrades MEA is carbonyl
sulfide (COS). MEA can, however, be regenerated by batch or continuous vaporization and disposal of the sludge formed by the degradation.
500
D.S.J. Jones and S.A. Treese