Brochure

18 | Fisher
®
Olefin Production Solutions
Rich Amine Letdown Valve
Before further processing, carbon dioxide (CO
2
) and hydrogen
sulde (H
2
S) are removed from the cracked gas. The presence
of H
2
S can cause serious corrosion issues, and CO
2
can freeze in
heat exchange and fractionation equipment. Acid gas removal
is accomplished by scrubbing with sodium hydroxide on a
once-through basis or in combination with a regenerative
solvent (amine).
As cracked gas enters the bottom of the acid gas scrubber and
ows upward, lean amine solution owing countercurrent strips
the gas of impurities. The rich amine letdown valve serves two
purposes. First, it regulates the level of rich amine solution that
accumulates in the bottom of the contactor vessel. Second, it
facilitates a pressure drop into the downstream ash tank, which
liberates a portion of the acid gases entrained in the solution. If not
addressed properly through detailed valve sizing and selection, this
outgassing of the entrained gases can cause signicant vibration
and damage to the valve.