31 / 100
HYDROCARBON
ENGINEERING
August
2019
29
A
n important aspect of the sulfur recovery/
amine-based tail gas treatment unit (TGTU) is to
maximise hydrogen sulfide absorption while
minimising carbon dioxide co-absorption.
Selective treating permits the full utilisation of the solvent
for hydrogen sulfide (H
2
S) removal by releasing the capacity
otherwise occupied by the carbon dioxide (CO
2
), thereby
reducing circulation rate and increasing efficiency. There are
currently two types of amine-based technologies used in
combination with sulfur recovery units:
methyldiethanolamine (MDEA) and sterically-hindered
amine such as FLEXSORB
TM
SE and SE Plus. This article will
present data to compare the stability and long-term
performance of both technologies in operating units.
Tail gas treatment and sulfur removal
efficiency
Over the past few decades, Claus type sulfur recovery
units (SRUs) have evolved to achieve increasingly greater
levels of sulfur recovery efficiencies (SRE), which have also
allowed facilities to meet lower sulfur dioxide (SO
2
)
emission targets. These improvements were partly made
possible by the introduction of solvent technologies
employed in the tail gas treatment section of the SRU.
Early Claus SRUs had no downstream technologies to
capture the remaining residual sulfur compounds exiting
the catalytic stages of the process. In a Claus SRU, H
2
S is
converted to elemental sulfur which can be used to make
fertilizers and other useful chemical compounds. Claus
SRUs typically convert 93 – 97% of the sulfur contained in
the feed streams to elemental sulfur.
1
TGTUs were later
added to SRUs to improve recovery and to reduce sulfur
emissions. Sulfur recovery and emissions are
interconnected in that sulfur that is not recovered in the
SRU is incinerated to form SO
2
. The acid gas from the
TGTU is recycled back to the SRU so that the overall SRE is
higher than what can be achieved with the SRU alone
(Figure 1).
Jenny Seagraves, ExxonMobil Chemical, USA, and
Robert B. Fedich, Essex Consulting, USA,
compare
amine-based tail gas treating technologies.