PSA Systems
Most modern hydrogen plants use pressure swing adsorption (PSA) systems. Refer
to the detailed PSA discussion in the section “Pressure Swing Adsorption” of this
chapter for information on critical aspects of PSAs.
Some specific areas to note about PSAs in the discussion are:
• Valves and sequence steps
• PSA adsorbers
• Off-gas/tail-gas drum
• Control system
Wet Chemical/Solvent Systems
Wet chemical or solvent CO 2 removal systems present their own challenges in
design. We will focus on amine solvent systems here, since they are most common.
Hot carbonate and other systems have some of the same issues, with slightly
different flavors.
A couple of the challenges considered here are:
• Corrosion management
As with most acid gas removal systems, metallurgy of the system needs to
consider the materials handled. Some specific considerations with hydrogen
plant systems are:
– Amine scrubbing solutions subject equipment to potential amine cracking.
Post-weld heat treatment of amine handling systems is advisable.
– The amine regenerator/CO 2 stripper tower and overhead are subject to carbonic acid attack. Stainless steel piping is needed.
– Carbonic acid attack is also seen in some unexpected places around the
stripper: shell near the reboiler return line and the piping and shell around
the stripper inlet line. It is advisable to consider alloying these areas and
watching the maximum velocities.
– In MEA amine systems, arsenic compounds may be used for corrosion
inhibitors. These are effective, but introduce an additional hazard during
operation and maintenance.
– Solvents tend to build heat-stable salts. These need to be eliminated to keep
the solution healthy. Some systems employ side-stream reclaimers to remove
the salts. They can also be removed by ion exchange using an outside service
company.
• Filtration
The circulating solvent streams will build up corrosion products and other solids,
in spite of corrosion inhibitors. These materials need to be removed from the
stream. This is normally accomplished by side-stream filtration of a slipstream
off the main circulating flow. The slipstream usually passes through a cartridge
filter and may also go through an activated carbon filter to remove potential
foaming materials or trace organics that you do not want in the solvent.
600
S.A. Treese
Most modern hydrogen plants use pressure swing adsorption (PSA) systems. Refer
to the detailed PSA discussion in the section “Pressure Swing Adsorption” of this
chapter for information on critical aspects of PSAs.
Some specific areas to note about PSAs in the discussion are:
• Valves and sequence steps
• PSA adsorbers
• Off-gas/tail-gas drum
• Control system
Wet Chemical/Solvent Systems
Wet chemical or solvent CO 2 removal systems present their own challenges in
design. We will focus on amine solvent systems here, since they are most common.
Hot carbonate and other systems have some of the same issues, with slightly
different flavors.
A couple of the challenges considered here are:
• Corrosion management
As with most acid gas removal systems, metallurgy of the system needs to
consider the materials handled. Some specific considerations with hydrogen
plant systems are:
– Amine scrubbing solutions subject equipment to potential amine cracking.
Post-weld heat treatment of amine handling systems is advisable.
– The amine regenerator/CO 2 stripper tower and overhead are subject to carbonic acid attack. Stainless steel piping is needed.
– Carbonic acid attack is also seen in some unexpected places around the
stripper: shell near the reboiler return line and the piping and shell around
the stripper inlet line. It is advisable to consider alloying these areas and
watching the maximum velocities.
– In MEA amine systems, arsenic compounds may be used for corrosion
inhibitors. These are effective, but introduce an additional hazard during
operation and maintenance.
– Solvents tend to build heat-stable salts. These need to be eliminated to keep
the solution healthy. Some systems employ side-stream reclaimers to remove
the salts. They can also be removed by ion exchange using an outside service
company.
• Filtration
The circulating solvent streams will build up corrosion products and other solids,
in spite of corrosion inhibitors. These materials need to be removed from the
stream. This is normally accomplished by side-stream filtration of a slipstream
off the main circulating flow. The slipstream usually passes through a cartridge
filter and may also go through an activated carbon filter to remove potential
foaming materials or trace organics that you do not want in the solvent.
600
S.A. Treese