Chemical Engineering April 2013 - 40

cover Story
feature report
Filtration and Separation
In Sulfur Recovery
Controlling contaminants
is key to reliable,
economical processing
across all segments
of industry
David Engel
Sulphur Experts, Filtration Division
S
ulfur is a major contaminant in
the oil and gas industry that exists
in various forms and requires
separation from both water and
process streams. In recent years the
removal of sulfur species has received
increasing attention because of safety
concerns, the need to reduce emissions
of sulfur oxides (SOx), and the fact that
sulfur harms the combustion properties
of fuels. The " sulfur recovery trail "
starts with hydrogen sulfide (H2S) and
mercaptans either present in raw hydrocarbon
streams or arising in the petroleum
refinery as a result of cracking
or hydrogenation processes. The trail
continues as H2S and mercaptans are
captured by methods such as amine
treatment, caustic scavenging, or sour
water stripping, and ends with the conversion
of H2S to elemental sulfur, sulfuric
acid, salts or other materials.
In the many plants that make up
the sulfur recovery trail, filtration and
other separation processes are important
in minimizing process upsets
caused by the presence of contaminants.
In fact, contamination control
through separation is a key step in
helping to maintain process control.
Separation processes are often the
first - sometimes the only - line of
defense for avoiding many process
variations and out-of-control episodes,
and separation devices play critical
roles in minimizing downtime and increasing
systems reliability.
Exploration and production
oil field/gas field
Amine
unit
Gas
plants
Refinery
Hydrotreater,
coker,
visbreaker,
catalytic cracker
Sulfur
reaction
plants
Sulfur
reaction
plants
Amine
unit
Sour
water
stripper
Residual
gas
treatment
Residual
gas
treatment
Figure 1. Typical stages of the sulfur recovery trail include (red) sulfur generation,
(green) sufur capture, and (yellow) sulfur reaction
Studies at a number of plants
worldwide reveal that many possess
less than adequate separation and
filtration systems, resulting in significantly
higher operating costs. Many of
the lessons learned along the sulfur
recovery trail about the need for good
separation are equally applicable to
other parts of the chemical process industries
(CPI).
Sulfur recovery Trail
Sulfur in hydrocarbons has two major
sources. It can be found naturally
as covalent sulfides in hydrocarbon
macrostructures, and it also occurs in
other chemical forms in crude oil, connate
water, produced water, natural
gas and gas condensates. New sulfur
species can also be generated when
crude oil is processed. For instance,
when water containing high levels of
sulfate is used to aid crude oil production,
sulfur reducing bacteria can turn
sulfates into H2S. In some cases, H2S
is produced by bacterial degradation
of organic matter.
Removal of H2S is accomplished
38 ChemiCal engineering www.Che.Com april 2013
without much difficulty by amine
systems, solvent systems, redox
(reduction-oxidation) reactions, precipitation
and chemical scavenging.
Mercaptans (also called thiols or, in
chemical shorthand, RSH), are somewhat
closely related to H2S and are
removed by fairly similar technologies.
However, sulfur species that are
covalently linked to organic systems
are not as reactive as H2S and need
to be transformed to H2S before they
can be removed.
One of the most common ways to do
this is through reduction with excess
hydrogen, using catalysts, heat and
pressure to drive the reaction to near
completion. This is the basis of catalytic
hydrogenation (also called catalytic
hydrodesulfurization), in which
sulfur residues (and to some extent nitrogen
residues) in hydrocarbons are
replaced by hydrogen. The sulfur combines
with excess hydrogen to produce
H2S, while nitrogen yields ammonia.
The resulting H2S-laden hydrocarbons
are purified alongside hydrogenated
hydrocarbons by amine
Mercaptan
removal
http://www.Che.Com
Chemical Engineering April 2013

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