Two stage sour water stripping
The unique advantage of the Chevron WWT
Process over conventional sour water
stripping processes is in producing separate high purity ammonia and hydrogen
sulfide products. As separate products both ammonia and hydrogen sulfide contribute
additional operational and economic value to refiners.
The Chevron WWT Process is a
two-stage stripping process that produces separate
ammonia and hydrogen sulfide streams from sour waters generated by process
units in petroleum refineries. The stripped water is suitable for reuse or
discharge through downstream treating facilities. The high purity hydrogen
sulfide is a premium feed to conventional sulfur recovery units or sulfuric
acid plants. The ammonia may be recovered for commercial sale or for internal
use. Alternatively, the ammonia may be separately incinerated.
Environmentally attractive...
Waste Water Treatment unit |
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Increasing legislative pressures are being exerted on the refining industry
to utilize “best available” technology for protection of the environment.
The WWT Process provides
the opportunity to economically treat refinery sour
waters while producing products that can be safely reused or discharged, sent
for further processing, or sold as end products.
Reuse of the WWT stripped
water is particularly attractive for two reasons.
First, it reduces refinery makeup water requirements. Second, it reduces the
overall waste water load on downstream treating facilities.
For difficult sour water feeds the WWT
Process often produces higher quality
stripped water than conventional sour water stripping. A difficult feed could
be sour water contaminated with organic acids.
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Improved performance of sulfur recovery units...
Separation of ammonia and hydrogen sulfide in a
WWT plant leads to more efficient
operation of sulfur recovery units (SRUs):
Where ammonia is completely removed from the SRU -
Eliminates ammonia-related problems such as:
- Lower operating factor
- Ammonia salt plugging in condensers and seals
- Catalyst deactivation
Where ammonia is ratably fed to the SRU -
The benefits to the SRU are:
- Higher operating factor
- Reduced catalyst deactivation
- Improved operating costs
- Improved ammonia destruction
As an additional benefit, incorporating a WWT
plant in a refinery processing
scheme is an excellent way to debottleneck an existing
SRU by removing the
ammonia from the acid gas feed. Furthermore, the elimination or control of
ammonia feed to the SRU increases the SRU
hydrogen sulfide capacity. This improvement
also can reduce the size of new SRUs
(Each one ton of ammonia removed from
the SRU feed adds
three tons of hydrogen sulfide capacity to the SRU.)
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Use of WWT ammonia for flue gas desulphurization to produce
saleable ammonium sulfate fertilizer...
A new recent application of WWT recovered ammonia is in flue gas desulphurization
using Marsulex technology. Marsulex is a leading provider of outsourced environmental
compliance solutions including traditional flue gas desulphurization systems.
The first application of the Marsulex ammonia-based desulfurization technology
using WWT recovered ammonia is
scheduled for start-up in 2004 by Syncrude
Canada Ltd. Syncrude Canada generates SOx from a Flexicoker and ammonia
from a LC Fining Unit.
Marsulex’ technology will use the WWT recovered ammonia to scrub SOx
from the Flexicoker flue gases to produce saleable high quality ammonium sulfate
fertilizer. The Marsulex ammonia-based flue gas desulphurization technology
has been in commercial service using commercially available ammonia since 1996.
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Ammonia recovery for commercial sale or internal use...
Ammonia separated from sour water can be recovered as a saleable product in
either the anhydrous or aqueous form. In some cases the ammonia can be utilized
within a refinery. Several WWT
operators use a portion of their WWT recovered
ammonia in Selective Catalytic Reduction/Selective Non-catalytic Reduction
Units. WWT ammonia can also be used
in the crude unit overhead to reduce corrosion.
Ammonia not sold or utilized may be separately incinerated.
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Hydrogen sulfide recovery for underground injection to enable
shut down of the SRU...
This novel concept represents a new potential
WWT application where the
WWT
recovered hydrogen sulfide is disposed by means other than as a feed to the
SRU. WWT's unique and
proven ability to produce a separate high purity
hydrogen sulfide stream from sour water allows this concept to be a reality.
The high purity of the WWT
recovered hydrogen sulfide reduces fouling and plugging
concerns for injection in a high pressure reservoir. The opportunity to shut
down or limit the use of the SRU
offers the potential for significant operating
and capital cost savings. This also gives the refiner the opportunity to discontinue
production of low value sulfur.