Solutions for a
e
r
u
t
u
f
r
e
n
a
e
cl
T
he world is quickly evolving towards the production
of low/ultra low sulfur, high quality fuels while at the
same time continually demanding reduced refinery
emissions. The key driver for these transformations is the
regulatory environment becoming increasingly stringent.
One direct consequence of required reductions in
emissions of criteria pollutants (SOx, NOx, VOCs, CO,
particulate matter and ozone) is that refiners are faced
with extensive capital investment to reduce emissions
and improve reliability of existing abatement systems,
including redundancy for sulfur gas recovery capacity.
It is also expected that the global refining community
will experience a general trend towards heavier, high
sulfur crude supply which will require further upgrades to
existing desulfurisation infrastructure and consequentially
additional sulfur gas recovery capacity as well.
A second direct consequence of required reductions
are the increased restrictions on mobile source
emissions of criteria pollutants, with the sulfur content of
transportation fuels being reduced to virtually zero. Use of
other gasoline blending compounds, such as aromatics,
Carlos Cavalca, Monty
Davis, Nick Confuorto,
Glenn Liolios, Tom
Hightower and Stuart
Thomas, DuPont Clean
Technologies, USA, discuss
integrated environmental
solutions for refinery
sulfur, nitrogen and clean
fuel challenges.
SAR-SGR acid plant - alkylation
integrated solutions
Figure 1. Onsite DuPont SAR-SGR sulfuric acid plant.
The picture on the right shows DuPont's Delaware City,
DE plant.
Figure 2. Onsite DuPont SAR-SGR sulfuric acid
plant integrated to a DuPont STRATCO® sulfuric
acid alkylation plant.
olefins, butane and, in some regions, oxygenates, are
also being restricted due to their impact on increased
higher criteria pollutant emissions. In the USA another
driver is the elimination of MTBE as a gasoline blending
compound, resulting in changes in fuel specification and
the increased use of ethanol, all of these resulting in
increased RFG demand.
All the above complex environmental and fuels
market dynamics, coupled with the intensification in
overall fuel demand coincident with the rapid economic
growth in several regions of the world (Asia Pacific,
Latin America, etc.) will require robust, integrated
sulfur management, emission control and clean fuel
environmental solutions to effectively address the
challenges associated with today’s low sulfur and high
fuel quality requirements.
Integrating environmental
solutions
DuPont Clean Technologies provides science based,
customised environmental solutions to refiners’
sulfur management, nitrogen management, emission
control and clean fuel needs. Today DuPont’s building
blocks for integrated environmental solutions include
DuPont Sulfur Gas Recovery (SGR) and Spent
Acid Regeneration (SAR) Technologies, DuPont™
STRATCO ® Clean Fuel Technologies, DuPont™
BELCO ® Clean Air Technologies and DuPont Clean
Water technologies.
Reprinted from HydrocarbonEngineering
DuPont’s sulfur management takes place
via an onsite SAR-SGR sulfuric acid facility
where DuPont builds, owns, operates and
maintains (BOOM) a sulfuric acid plant
located on or adjacent to a refinery, as
shown in Figure 1. The objective of this
plant is to provide total or partial sulfur gas
recovery (SGR) to the refinery, including
SRU backup, in addition to alkylation spent
acid regeneration (SAR) service. Process
design improvements make investment in
new onsite acid plants a viable alternative
to Claus with tail gas treatment. The acid
plant is designed to optimise the conversion
balance of refinery sulfur gases and
alkylation spent acid, as the acid gas is
used as the fuel in the spent regeneration
process. Sulfur gases include amine gas,
tail gas, SWS gas, gasifier acid gas, and
stack scrubbed gases. The DuPont plant
can also process a variety of chemical spent
sulfuric acid. In addition, the operating
philosophy and reliability of the SAR-SGR
plant is consistent with refinery turnaround
schedules. Furthermore, benefits of on-site
SAR arrangements at the refinery include
no logistics issues for spent acid (e.g.
elimination of transport of spent acid offsite),
management of acid gas for the refinery and
high pressure steam production. Figure 1
shows DuPont's Delaware City, DE SAR-SGR
plant. Two more similar facilities are currently
under construction in El Paso, Texas, and
Linden, New Jersey.
DuPont™ STRATCO® Clean Fuels Technologies
are based on STRATCO® sulfuric acid alkylation
technology. One of DuPont’s strategies for clean fuels
involve the production of alkylate. Alkylate enjoys
inherent advantages, such as high RON and MON with
low sensitivity, negligible amount of sulfur, olefins,
aromatics/benzene and can be produced to low RVP.
When compared to other olefin upgrading processes
(such as ETBE, dimerisation, etc.) alkylation offers
overall improved yield (as volume product/volume olefin
used) and improved RON & MON numbers. STRATCO®
sulfuric acid alkylation is the safest, proven alkylation
technology and is being constantly improved through
DuPont R&D programmes and operating experience.
The effective integration of this state of the art
alkylation technology with DuPont’s SAR-SGR offering
allows the optimisation of synergies between processes,
thus allowing lower energy costs, reduction of capital
investment, and improved operational flexibility for
alkylate production and sulfur gas recovery (including
processing of amine gas and sour water stripper
gas). Examples of synergies of integration for these
systems include, for example, elimination of redundant
equipment, such as neutralisation systems between
units, minimising capital investment. Another example
is the supply of steam for the alkylation unit deisobutaniser column by the SAR-SGR acid plant
optimising operating cost and energy integration as
August2007
www.hydrocarbonengineering.com
well as varying the rate of fresh acid supply to
the alkylation unit by the SAR plant to optimise
alkylate product octane properties.
In this integrated sulfur managementalkylation conversion configuration DuPont
can BOOM both the SAR-SGR and sulfuric
acid alkylation plants located on or adjacent
to a refinery. In addition to sulfur recovery,
DuPont can conduct toll (fee-based) conversion
of refinery-owned alkylation feedstocks,
returning to the customer alkylate product and
byproducts. As DuPont toll-alkylates feeds for
the refinery, the spent acid regeneration is now
‘invisible’ to the customer. Figure 2 depicts this
integrated solution.
When this integrated model is deployed
Figure 3. Regional onsite DuPont SAR-SGR - alkylation plant.
regionally, by consolidation of alkylation
feeds from multiple refineries into a regional
alkylation-SAR-SGR installation, improved
Figure 4. DuPont modular plant for on-site
economies of scale driven by the increased
NH3 SWS gas scrubbing and ammonium
size of the alkylation plant can enable alkylation
sulfate production.
of feedstocks for a number of refineries.
Harnessing of this alkylation economy of scale
can result in lower per unit alkylation costs.
This regional SAR-SGR-alkylation model is
particularly applicable in situations where
local refineries do not have enough alkylation
feedstocks to justify an alkylation unit and/
or where economies of scale of a smaller
unit makes owning an alkylation plant not
economically feasible.
In this business model, depicted in Figure 3,
a regional DuPont BOOM SAR-SGR-alkylation
unit is deployed in a host refinery where the
larger alkylation and SGR-SAR acid plant is
built, providing not only toll alkylation and SGR service
downstream problems in the SRU due to nitrogen salt
to the host refinery but also toll alkylation service
formation. By elimination of ammonia from the Claus
for feedstocks from regional refineries. Alkylation
feed, ca 3.75 t additional sulfur processing capacity per t
feedstocks and alkylate product for these regional
of ammonia removed can be gained. This also provides
refineries can be transported by truck, rail or marine.
for elimination of SWS NH3 separation costs and
elimination of ammonia incineration and associated SOx
Ammonia SWS gas recovery - SGR acid
emissions linked with the incineration of H2S-containing
plant integrated solutions
NH3 streams.
DuPont recently developed a technology to separate
As the process of ammonia recovery from the
sour gas stream requires sulfuric acid, this SWS gas
and process ammonia from sour water stripper (SWS)
gas. This technology is very suitable for refineries that
scrubbing plant can be integrated to an on-site SGR
process crudes with a high level of nitrogen-bound
sulfuric acid plant which can provide sulfur management
species and/or larger amounts of sour water. The former
to the host refinery. This SGR plant can convert sulfur
is particularly true in Central and South America, where
gases into sulfuric acid product, providing incremental
the indigenous crudes are typically high in nitrogen, for
or total sulfur recovery capacity and/or SRU backup
example, Marlim (Brazil) containing 4900 ppmw N and
to the refinery and non-fuming sulfuric acid to the NH3
Maya (Mexico) averaging 3600 ppmw N.
scrubbing/ammonium sulfate plant. It should be noted
In this technology, ammonia in the SWS gas
that this ammonia scrubbing plant can be fed with a
is converted into ammonium sulfate solution by
variety of acid strengths, including diluted (waste) acid
scrubbing the sour gas with sulfuric acid and by steam
streams from the SGR plant, thus maximising the usage
stripping the liquid sulfate product of residual H2S and
of sulfur streams. Figure 5 presents the integration
mercaptans. The ammonia free, dry SWS scrubbed gas
concept for this installation.
containing 90%+ H2S can be fed into a Claus unit or
Taking into consideration factors such as capital
a SGR sulfuric acid plant while the ammonium sulfate
required to BOOM an SGR acid plant, availability of
liquor product can be used as a green (non-hydrocarbon
spent acid and availability of acid gas and sour water,
derived) nitrogen fertiliser feedstock (Figure 4 depicts
the optimal, most cost effective configuration for
the process).
integration of this type of technology may be a cluster
This technology of refinery nitrogen management
of NH3 scrubbing/ammonium sulfate plants located
allows improved Claus capacity and minimisation of
strategically at nearby satellite refineries with a single
www.hydrocarbonengineering.com
Reprinted from August2007
HydrocarbonEngineering
Figure 5. NH3 SWS gas scrubbing/ammonium sulfate - SGR sulfuric
acid plant integrated installation concept.
Figure 6. DuPont onsite integrated SO2 scrubbing - SGR sulfuric acid
plant facility.
Figure 7. DuPont onsite integrated SO2 scrubbing - SGR-SAR sulfuric
acid – alkylation installation.
DuPont BOOM SGR sulfuric acid plant located at a host
refinery converting acid gas into sulfuric acid to supply
the network of ammonium sulfate plants. The logistics
of acid transport and uptake of ammonium sulfate
product to/from the nearby satellite refineries will also
be an important factor when considering this option.
Figure 5 shows this distributed NH3 SWS gas scrubbing/
ammonium sulfate model.
SO2 scrubbing - SGR-SAR acid plant alkylation integrated solutions
Conclusion
The effective integration of sulfur management,
nitrogen management, emission control and clean fuels
technologies allows the creation and implementation of
innovative environmental solutions that:
l Optimise synergies between technologies.
l Offers the lowest environmental footprint.
l Maximises benefit to the refiner.
Notes
DuPont™ BELCO® Clean Air Technologies are based
on world class scrubbing technologies for abatement
of SOx, NOx and particulate matter emissions from
refinery processes. BELCO® provides an extensive array
of proven scrubbing solutions (standard, such as the
EDV® Wet Scrubbing System, or regenerative, such as
LABSORB™) for refinery FCCU, coking units, power
Reprinted from HydrocarbonEngineering
boilers, fired heaters, etc. The EDV® scrubber can also
be integrated with the LoTOx™ process for additional
control of NOx emissions. For applications with very
high levels of SO2, such as fuel switching in boilers or
power plants where lower cost high sulfur fuels can
be used instead of natural gas or sulfur-lean fuels, or
for those applications where disposal of liquid or solid
scrubber byproducts are an issue, BELCO® provides
Dual Alkaly and LABSORB™ scrubbing technologies.
Strong synergies exist between the regenerative
LABSORB™ system and the DuPont SGR sulfuric
acid plant offering. In cases where a LABSORB™
regenerative scrubbing system is deployed to clean
FCCU flue gases or boiler/power plant exhaust (typically
when the refinery is faced with requirements of minimal
solids or liquid byproducts discharge), the regenerated,
concentrated, SO2 stream from the LABSORB™ stripper
column can be sent to the DuPont SGR plant for
conversion into sulfuric acid product. In this integrated
configuration, operating costs can be reduced if the
steam generated in the SGR plant can be sent back to
the LABSORB™ system to be used in the regeneration
process. For this application the design of the SGR
acid plant could be simplified (with a resultant reduction
in capital investment) if the only source of sulfur is
SO2. Finally, this integrated configuration allows the
straightforward conversion of waste SO2 into a valuable
commodity, sulfuric acid, instead of conversion into
sulfur in a Claus unit requiring H2S feedstock. Figure 6
shows the LABSORB™ regenerative scrubber-SGR acid
plant integrated concept.
Finally, the optimal combination of synergies for
the integration of DuPont environmental solutions can
be found on the DuPont onsite scrubbing, SAR-SGR
sulfuric acid, toll alkylation configuration. In this full
integration case the design of the acid plant is optimised
by the presence of spent acid, acid gas and scrubber
sulfur dioxide streams, with the design of this unit being
simultaneously optimised with the design of the alkylation
unit and scrubber system. The synergies derived from
the full integration of the above solutions translate into
lower capital investment, overall lower operating costs,
improved environmental footprint (lower emissions) and
improved sulfur recovery/toll alkylation benefits to the
refiner. Figure 7 presents this full integration concept.
DuPont™ BELCO ® and BELCO ® are trademarks of BELCO
Technologies Corp.
LABSORB™ is a trademark of BELCO Technologies Corp.
EDV® is a trademark of BELCO Technologies Corp.
LoTOx™ is a trademark of the BOC Group, Inc.
The LoTOx™ process is available exclusively for FCCU and Fluid
Coker applications from BELCO® under license from BOC.
DuPont™ STRATCO® and STRATCO® are trademarks of DuPont.
August2007
www.hydrocarbonengineering.com