Hydrocarbon Processing - December 2022 - 50

Process Optimization
Sulfuric acid is recycled to the Claus
furnace and the key chemical reactions
are included here.
The consideration of dilution gas is
worth noting. In the overall Claus reaction,
there are 12 moles of dilution gas for
every four sulfur atoms produced. Using
pure oxygen rather than air, the nitrogen
is removed, leaving just four moles of
dilution gas. Recycle acid is an excellent
oxygen carrier and leads to only 4.4 moles
of dilution gas, facilitating the reduction
of air demand to ~20%. Another comparison
with a conventional TGTU is that
there is no CO2
in the recycle stream to
the furnace. These factors contribute to a
capacity increase in the Claus section.
Key questions arising from this are
how quickly liquid acid would be vaporized;
how quickly the gas would disassociate;
and how quickly the standard Claus
components would be formed. These
questions were investigated independently
by Alberta Sulfur Research Ltd.
(ASRL) and HEC Technologies and answered,
as shown in FIG. 3.
Particularly for refinery applications,
an alternative for processing SWS offgas
with the new sulfur recovery processa
becomes apparent. Traditionally, these
gases-which contain ammonia, hydrogen
sulfide and water vapor-are routed
to the front section of a two-stage Claus
thermal reactor operating at 1,250°C to
ensure the complete destruction of ammonia.
Inadequate ammonia destruction
(e.g., in a single combustion zone thermal
reactor operating at ~1,000°C) can lead
to ammonium salt deposition at the final
condenser, especially when cooled using a
1-barg closed-loop cooling arrangement.
The new sulfur recovery processa
configuration
allows routing of the SWS gases
directly to the combustor in the WSA
section, as shown in FIG. 4, simplifying
the Claus section and avoiding the potential
deposition problem. The SWS gas is
burned in the combustor of the WSA section
with excess air. This leads unavoidably
to some formation of nitrogen oxides
(NOx
), which are removed again in the
SCR reactor located after the waste heat
boiler. A small fraction of the SWS gas is
added to the combustor effluent after the
waste heat boiler to provide enough ammonia
to react with the formed NOx
over
the catalyst installed in the SCR reactor.
The results of the reaction are nitrogen
and water vapor.
50 DECEMBER 2022 | HydrocarbonProcessing.com
The feasibility of this concept, however,
must be evaluated in each individual case
and depends on several factors, such as:
* The ratio between amine acid
gas (i.e., with no ammonia
present) and SWS gas flows
* The required overall SRE
* The possibility of exporting
a certain amount of sulfuric
acid as a separate product.
Often, it will be necessary to have the
SWS gas processed in the Claus section.
Takeaway. The new sulfur recovery processa
achieves
a sulfur recovery equivalent
to the conventional design, is a simpler
process with fewer parameters to
control, and the economic benefits are
substantial. The Claus unit itself will be
smaller due to the recycle and oxygen
carrying capacity of the acid.
Additional flexibility can be provided
by producing a small sulfuric acid stream,
which could be useful in a refinery application,
though special circumstances
would be required to progress this route.
Maintaining a single product stream is going
to be preferable in most applications.
Brownfield applications (i.e., revamps)
provide unique opportunities,
with perhaps limited space, a need for
increased capacity, and a requirement to
meet increasingly tight emissions specifications.
The WSA section can be constructed
while the Claus unit is in operation,
so it provides minimum shutdown
time, minimum personnel onsite and
simultaneous operations (SIMOPS) advantages,
in general.
The application to natural gas plant
SRUs affords some enhanced benefits for
the sulfur recovery processa
, including:
* Significant CO2
in the feed reduces
the thermal reactor temperature
and increases the size of the
conventional TGTU
* CO2 co-absorbed in aminebased
TGTUs is recycled to
the inlet of Claus unit
* TGTU amine requires leaner
loading to allow CO2
" slip "
* All CO2
the stack
passes through to
* Smaller recycle = smaller SRU
* Simple, robust and efficient
* Sulfur recovery of > 99.9%
with all sulfur compounds
converted into elemental sulfur
* Flexibility in production
* All product is elemental sulfur
* Reduced Claus unit size due to
sulfuric acid recycle, providing a
degree of oxygen enrichment
* No waste streams
* Feasible solution for both greenfield
and brownfield applications
* High thermal efficiency
with HP steam export
* Integrated efficient features
of WSA with the sulfurproducing
Claus process
* Based on proven technologies with
integration demonstrated by ASRL.
Parts 2 and 3 of this article will appear
in subsequent issues of Hydrocarbon Processing
and will cover environmental and
economic aspects, respectively.
NOTES
a TopClaus®
b Comprimo's SuperClaus®
JON LEWIS leads UK Operations
for Comprimo, part of the Worley
group, after serving as Global
Director for gas processing. Lewis's
responsibilities span consultancy,
project delivery, client support and
business development. He has
extensive conceptual and detailed engineering
experience and has held various roles associated
with gas processing terminals, offshore platforms
and refineries in his 29-yr career with the company,
as well as managing the London Process Department
from 2004-2011. Lewis graduated with an MS degree
in advanced chemical engineering from the
University of Manchester (UMIST) in the UK, is a
Chartered Engineer and Fellow of the Institute of
Chemical Engineers (FIChemE), and has published
articles and presented at international conferences.
After graduation as chemical
engineer, FRANDS E. JENSEN has
been working for Topsoe since
1979 in various marketing and sales
positions and has been dealing
with most of the technologies
offered by Topsoe. Since 2003,
Jensen has concentrated on the WSA, SNOX™ and
TopClaus® technologies applied for sulfur removal
from offgases as Senior Sales Manager.
HESBON NJUGUNA is a Principal
Process Engineer at Comprimo,
part of the Worley group, and has
extensive experience working in the
design of sulfur recovery plants
constituting the Claus process,
SWS, amine regeneration and
TGTUs throughout his 15-yr career with the company.
Njuguna has been heavily involved in the early
development of the TopClaus® technology. He
graduated with an honors degree in chemical
engineering from the University of Nottingham in the
UK and earned an MS degree in forensic engineering
and science from Cranfield University in the UK.
Njuguna is a Chartered Engineer and Member of the
Institute of Chemical Engineers (MIChemE).
http://www.HydrocarbonProcessing.com
Hydrocarbon Processing - December 2022

Table of Contents for the Digital Edition of Hydrocarbon Processing - December 2022
