Technical
Paper
Outsourcing Eliminates Hazardous
Regenerant Chemicals at TVA
Summary
Objectives were established to improve cycle chemistry, to lower the overall cost of treatment, and to
meet TVA’s “Environmental Leadership” corporate
goal by improving make-up water treatment and
condensate polisher performance. This paper discusses the fundamental design criteria and operational results of off-site condensate polishing resin
regeneration by service contract. Also presented
are how off-site ion exchange resin regeneration is
used in combination with new make-up treatment
technologies, and outsourced equipment and services, to reduce wastewater discharge of regenerant chemicals and meet the objectives.
Introduction
In 1993, Tennessee Valley Authority’s (TVA’s) Board
of Directors established “Environmental Leadership”
as one of the company’s primary corporate goals.1
Regenerant chemicals and the corresponding
wastewater discharge were identified as a source
for potential adverse environmental impacts. Environmental concerns, along with increasing operational and maintenance costs, lead TVA
management to specify the elimination of hazardous regenerant chemicals from TVA fossil plants.
This eliminated the use of acid and caustic for the
regeneration of ion exchange resins used for condensate polishing and make-up demineralization.
Make-up water treatment by service contract (outsourcing) has become commonplace in the electric
utility industry. The benefits of improved economics
and water quality, allow the utility to refocus resources on power generation and streamline plant
performance to remain competitive in a deregulated marketplace.2, 3 Membrane and electrochemical technologies are leading the charge to eliminate
hazardous regenerant chemicals for make-up water production. This combination of electric and
pressure driven technologies presents end users
the opportunity to process raw water and purify to
ultrapure water quality, without hazardous chemicals.
Condensate polishing by ion exchange is still the
workhorse technology in the industry. Conventional
deep bed condensate polishing requires chemical
reactivation prior to reuse, which has traditionally
been performed at individual generating stations.
With requisite chemical regeneration, TVA was presented with a significant challenge to eliminate
regenerant acids and caustics in their fossil plants.
Temperature and pressure requirements, the low
ionic challenge, characteristics of the ionic species,
and the nature of potential foulants in a condensate
source eliminate the current generation of membrane and electrochemical technologies as an
alternative to conventional ion exchange designs.
Given that a non-regenerable or disposable bead
ion exchange condensate polishing system in a fossil plant is an uneconomical option, TVA’s sought to
execute the condensate polisher regenerations at
an external facility.
After evaluating options, Tennessee Valley Authority
entered into a Partnering Agreement with GE Power
& Water, a global high purity water treatment services company, to achieve these goals. A primary
emphasis of this paper is to introduce off-site condensate polishing regeneration services as a qualified alternative for electric utility generators and
plant designers to eliminate the negative impacts of
on-site resin regeneration. Topics include required
modifications to existing TVA equipment, design
and operating criteria, improvements in cycle
chemistry; other factors which affect operational
costs and influence the economic decision to outFind a contact near you by visiting www.ge.com/water and clicking on “Contact Us”.
* Trademark of General Electric Company; may be registered in one or more countries.
©2010, General Electric Company. All rights reserved.
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source off-site regeneration of bead condensate
polishing resin. Also presented are the membrane,
electrochemical and conventional ion exchange
technologies employed by the service company to
improve make-up quality, while enabling TVA’s fossil
plants to become hazardous regenerant chemicalfree.
Expanding Outlook
Environmental considerations are influencing the
way corporations do business. Water intake, recycle/reuse and wastewater discharge regulations
are a prime consideration in planning, permitting
and constructing new power plants. Moreover,
existing plant operations are not immune from
tightening environmental regulations. There is a
growing awareness and examination of individual
trace impurities in an industrial discharge stream,
which are, or could be, classified as pollutants. As
Strauss notes, as the activist political climate for
environmental concerns continues to grow, how
long will it be before the focus of activist groups
shifts from protesting construction of new installations to ongoing operations at existing power plants? 4
Today’s reality is that hazardous chemicals and
wastewater issues are in the spotlight, and industry
will bear more pressure to reduce wastewater generation at the “source,” or to implement costly endof-pipe treatment. The current trend is to shift
major decisions affecting the environment away
from the plant’s environmental engineer and senior
management to the Board of Directors. This shift in
decision-making is driven, in part, by the fact that
current and future environmental liabilities are
reported on a company’s balance sheet, and thus
can adversely affect the ability of a business to
attract investor capital. Indeed, as we have one eye
focused on improving water quality for highpressure steam generation systems, we must also
look at how these improvements will effect current
and future wastewater discharge requirements.
TVA’s corporate decision to eliminate regenerant
chemical use and wastewater discharge represents
a proactive leadership role in environmental matters. This decision may also position the utility to
mitigate any adverse effects of uncertain future
wastewater discharge regulations.
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Condensate Polishing
To drive the power producing turbine and generator, copious volumes of water are converted to
steam which expends its energy in the turbine, is
condensed in a heat exchanger (condenser) and
returned to the boiler or steam generator. In facilities with supercritical high pressure boilers, oncethrough steam generators (OTSG), nuclear generating stations (PWRs and BWRs), and a greater number of high pressure drum boilers, this condensate
must be “polished” to remove trace contaminants
to achieve the required purity before it can be
recycled.5 Ion exchange technology, using powdered resin or deep bed systems, accomplishes this
repurification by removing particulate and nonionic matter by adsorption or mechanical filtration,
and exchange of dissolved ionic material. The
design objectives of condensate polishing systems
are to protect the steam generator from a condenser leak, and produce a reliable, high quality
treated return condensate. While the powdered
resin is discarded after use, the deep bed system
requires chemical regeneration before reuse and is
the subject of further discussion.
The commercial dates for TVA’s eleven fossil plants
range from the early 1950s to the early 1970s.6
Condensate polishing equipment was not included
with any of TVA’s drum-type fossil units, while all of
the OTSG designs are equipped with condensate
polishing equipment. The four (4) TVA fossil generating stations (six (6) generating units) with deep
bed condensate polishers are:
1. Bull Run Fossil, Clinton, TN
2. Colbert Fossil, Tuscumbia, AL
3. Cumberland Fossil, Cumberland City, TN
4. Paradise Fossil, Drakesboro, KY
All polisher designs include “naked” mixed beds.
The four plants did not use any special techniques
or equipment to improve resin separation. At Paradise and Colbert Fossil, the resins were backwashed, separated, regenerated, mixed and rinsed
in one vessel. Cumberland and Bull Run Fossil used
conventional external separation and regeneration
equipment. In the external design, exhausted beds
are transferred from the service vessel to a
separation vessel, where the cation and anion resins are classified into individual components. The
anion portion is transferred into another vessel for
caustic regeneration, while the cation resin typically
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undergoes an acid regeneration in the separation
vessel. The regenerated resins are then re-mixed
and transferred to “clean” storage or returned
to service.
External Regeneration, Very External
Off-site regeneration requires the exhausted bed be
moved into resin storage vessel, or transferred
directly to a transportation unit for delivery to GE’s
centralized regeneration facility located in St.
Peters, MO. It is obvious that the service contract
does not eliminate the requirement for condensate
polisher chemical regeneration, but it does shift the
chemical storage, handling, regeneration and
wastewater discharge to an external location. Of
course, like a power plant, a service company must
meet current and future wastewater discharge
regulations. But a properly positioned service provider can alleviate these issues by location in an
area with the infrastructure and treatment technology to handle ion exchange regenerant wastes. In
addition, consolidation of TVA’s regeneration
requirements at its St. Peters plant enabled GE to
design and install advanced wastewater treatment
technologies specifically engineered to process
impurities from condensate polisher regenerations.
Regeneration Facility
The St. Peters Regional Plant, located 15 miles
northwest of St. Louis, MO, began operation in
January 1999 (Figure 1). The 48,000 square foot
facility has more than 25,000 square feet dedicated
to ion exchange resin processing and regeneration.
Figure 1: St. Peters Regional Plant
Exhausted resins are physically inspected on arrival
at the regeneration facility prior to processing. The
purpose of this inspection is to obtain a gauge on
the required cleaning, if the presence of crud or
other resin foulants is detected. The exhausted resin
is then transferred from the transportation vehicle
to resin cleaning equipment. This equipment is custom designed and built to optimize results from GE’s
proprietary physical and chemical resin cleaning
procedures. Segregated separation equipment and
proprietary separation techniques minimize resin
cross contamination, which is the most important
step to minimize ion leakage and achieve a high
purity effluent. The separated cation and anion
segments are transferred to dedicated cation and
anion regeneration vessels for chemical reactivation. After regeneration to the H+/OH- cycle, the resins are mixed and transferred to clean resin
storage, or directly to the transportation vehicle.
An inventory of replacement resin is maintained at
the service provider’s facility to adjust to the correct
volumetric resin ratio before regeneration.
Resin Selection
Simplicity, consistency, and the flexibility to service
multiple generating stations; all are reasons TVA
elected to standardize on one condensate polishing
resin manufacturer and type. Standardization also
enabled the service company to avoid maintaining
an inventory of multiple manufacturers and resin
types. TVA selected a uniform particle size (UPS),
10% DVB, gellular strong acid cation resin, and a
macroporous, Type 1, strong base anion resin
(Rohm and Haas Amberjet 1500 and Ambersep 900,
respectively). This resin combination facilitates
separation by the difference in terminal settling velocities between the cation and anion resin. A 1:1
volumetric resin ratio (approximate 2:1 equivalent
ratio: cation to anion) is the service charge delivered
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to each facility. TVA’s resin selection was based on
empirical data: what resins give the best results in
field performance in their units.
Delivery Vehicle
The bulk resin is moved between TVA sites and the
regeneration facility by a Heil tank type trailer (Figure 2), co-designed by TVA and GE. The unit has
volume capacity of 1500 ft3 (42 m3), but highway
weight limitations restrict transport volume to
approximately 1200 ft3 (34 m3). Isolated compartments permit the unit to carry a mixture of “clean”
and “dirty” resin without intermixing. These compartments allow one trailer to service one or more
plants in a single trip. Isolated compartments also
enhance resin transfer and aid in complete
resin removal.
Figure 2: Transportation Vehicle
Each compartment is equipped to receive air or
water pressure (or both) to fluidize and move the
resin. A custom underdrain design facilitates resin
movement, and allows the sluice water from a
“dirty” bed to drain to waste. The prototype Heil
trailer was purchased and transported by TVA.
Required Modifications
Bulk Storage
Storage capability for both “clean” and “dirty” resin
is a practical requirement at the power plant for offsite condensate polishing regeneration by service
contract. The required holdup volume of both
exhausted and regenerated resin is an important
plant decision. The bed exhaustion schedule,
response record of the service provider, regeneration and transportation time and the total resin
“float” volume all merit consideration to determine
the required storage capacity for each plant.
Economics and risk assessment also play a major
role to determine the required safety margin to proPage 4
tect against a condenser leak. Undoubtedly, spare
charges of regenerated resin stored at the owner’s
facility provide the best protection against unexpected problems.
TVA operates with a minimum one spare charge of
regenerated resin onsite per operating unit. At least
one additional bed is in transportation or regeneration at the service provider’s regeneration facility.
As is typical, the plants originally had little condensate resin storage capacity. To achieve the desired
storage volume, TVA retrofitted existing vessels and
installed new storage vessels.
Resin Transfer
Design changes were required for the transportation vehicle loading and unloading area, referred to
as the “transfer area.” Plant modifications include a
supply of the following to the boundary of the transfer area:
•
Pressurized demineralized water
•
Pressurized oil-free plant air
•
Transfer piping for regenerated resin
•
Transfer piping for exhausted resin
•
Wastewater piping
GE personnel trained TVA plant operators in pneumatic and hydraulic transfer techniques to sluice
resin to and from the transport trailer and the
appropriate storage vessels. Transfer distances are
300 to 400 feet (91 to 122 meters), at up to 100 feet
(30 meters) elevation. The typical time to unload a
trailer is one to two hours, including set-up.
Paradise Condensate Polisher System
Commissioned in 1963, TVA’s Paradise Fossil Plant
has 625 MW generating capacity, using two (2)
cyclone-fired Babcock & Wilcox subcritical 2,400 psi
OTSG’s. The full-flow deep bed condensate polisher
system consists of:
•
•
•
•
•
3 x 100% vessels; 2400 gpm (545 m3/h) per vessel
100 psi ASME
300 ft3 (8 m3) bed volume per vessel
2 x 300 ft3 (8 m3) clean storage vessels
2 x 300 ft3 (8 m3) dirty storage vessels
Oxygenated feedwater treatment (OT) is regulated
between 50-150 ppb at the boiler feedwater
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pumps, with ammonia and oxygen treatment
chemicals added to the OTSG feed. The average
ammonia challenge to the condensate polisher is
0.1 ppm at a pH between 8.7-8.8.
Results At Paradise
TVA has always practiced tight cycle chemistry at
Paradise Fossil Plant. The strict criteria for taking a
bed out of service remained unchanged after initiation of contract regeneration services in 1998:
•
Sodium (Na+)
0.5 ppb
•
Specific conductivity
0.1 micromho/cm
To establish and maintain a routine off-site regeneration schedule, the service company exchanges
one (1) bed per week. Two regenerated beds are
maintained in clean resin storage at Paradise Fossil
as an additional safety factor for the two unit generating station.
Average bed throughput has increased over 33
percent after commencement of off-site condensate polishing (Figure 3). Since establishing routine
service, only one (1) bed was removed from service
because of control set points. The balance of the
beds have been changed out according to schedule
(e.g. they could have run longer than 120 million
gallons).
trained and skilled in resin transfer. Precautions in
vessel loading to avoid bed stratification and the
complete removal of exhausted resin from the service vessels (to avoid the dreaded heel affect) is also
crucial in the production of low sodium demineralized water, not to mention reliably producing parts
per trillion sodium.
Table 1: Typical Polisher Effluent Quality
Economic Influences
Transportation distance and bed throughput are
two influential factors in the operational expense of
off-site condensate polisher regeneration services.
While the former can be considered a constant
(Figure 4), bed throughput is influenced by many
different factors:
•
Quality requirements
•
Operational cycle (H+/OH- vs. NH4+/OH-)
•
Ionic loading (boiler chemistry and condenser
leaks)
•
Deep bed design (SAC/MB vs. “naked” MB)
•
Particulate (crud) load and other potential
resin foulants
Figure 3: Off-site condensate polishing
The most important factor in achieving low contaminant levels is the diligence of qualified equipment operators in handling the resins, both at the
generating stations and the off-site regeneration
facility. The effluent quality detailed in Table 1 is a
reflection of the high efficiency separation, cleaning
and chemical regeneration techniques performed
by the service provider. TVA personnel are highly
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Figure 4: Mileage to Regeneration Plant
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Boiler pressure and limitations on feedwater contaminants dictate quality requirements. OTSG units
require full-flow polishing to control contaminants
and maintain ultrapure feedwater quality. There is a
strong interconnection between effluent quality and
the resin bed ionic form. The H+/OH- cycle
results in the highest effluent quality and achieves
maximum protection from a condenser leak, albeit
at the sacrifice of bed throughput if not run past the
ammonia break. For a given target effluent sodium
and chloride concentration, higher resin conversion
rates are required for operation in the NH4+/OHcycle; thus, the benefit of longer bed runlengths is
offset against increased chemical consumption and
cost. TVA operates their condensate polishers in the
H+/OH- form, and does not run past the ammonia break.
Steam cycle chemistry and feedwater treatment
determine the ionic challenge to the polisher system in the absence of air ingress and condenser
leaks. Paradise practices oxygenated feedwater
treatment (OT) with ammonia to control pH.
Ammonia represents the major cationic load on the
polisher because it volatizes with the steam and
returns in the condensate. Cycle chemistry and pH
influence the ionic challenge to the resin and affect
bed throughput, thereby influence economics.
Resin fouling leads to reduced bed throughput and
a higher bed exchange frequency. In the absence of
a lead cation bed or prefiltration, particulate is
deposited directly on the mixed bed resin. If
severe, crud loading can cause a bed to be taken
out of service on pressure drop before full utilization
the operational capacity. Difficult resin separation,
resin fouling and reduced capacity all can result
from crud loading. It is well known that corrosion
byproducts from the boiler and steam cycle components apex after idle periods. During unit startup, disruption of passive metal layers and corrosion
products can result in these high crud loads. TVA
protects the polishing resin from high crud loading
at unit start-up with coated pre-filters.
Fouled resin can also result from sealant or lubricant leaks, and contamination due to system maintenance. Regardless, abnormal crud loads or other
resin fouling mechanisms will cause laborious
scouring and extended cleaning procedures and
may dictate elevated regenerant levels to restore
resin operational capacity. Therefore, avoiding resin
fouling and requests for partial deliveries saves on
the cost of treatment.
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Rise Of The Membrane Processes
Condensate polishing is one determining factor in
feedwater purity; the second is make-up water
treatment. One can argue the most exciting developments in water treatment are the new technologies applied in current make-up systems. The
development and advancement of membrane
separation processes have fathered these new
generation treatment technologies. Today, there
are membrane processes available to replace classic treatment technologies for virtually every component in a water treatment system. Not only can
membrane processes produce superior water quality (used alone or in combination with chemically
driven technologies) they also offer the opportunity
to process raw water to ultrapure quality, with no
regenerant chemicals.
The “total cost of ownership” analysis for a water
treatment system has evolved to include contract
services versus capital purchase, and conventional
chemical versus electrochemical and mechanical
membrane purification technologies. Although still
valuable, fading are the days of solely relying on
spreadsheet calculations to indicate the system
with the lowest cost of ownership to determine
equipment selection. Environmental considerations
are commanding a larger role in the decision process, dictating wastewater concerns be evaluated
along with economics.
Make-Up Demineralization
TVA performed such an analysis to decide how to
meet its demineralized make-up water requirements. The details of this analysis have been presented in prior work.7 TVA selected a “hybrid”
combination of TVA owned equipment and contract
services to meet the make-up requirements for five
(5) of TVA’s eleven fossil facilities. Necessary design
modifications and unexpected and unbudgeted
cost overruns for the capital equipment resulted in
an estimated cost to produce demineralized makeup water 30% to 60% higher than the fixed cost
quoted by the service provider. TVA has since
entered into a Partnering Agreement with the service provider to build, own, operate and maintain
(BOOM) the high purity demineralized water
make-up systems for the remaining six (6) fossil
plants and TVA’s three (3) nuclear plants.
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Membrane based separation technologies included
in the service provider’s make-up systems include:
•
Microfiltration (MF)
•
Reverse Osmosis (RO)
•
Gas Transfer Membranes (GTM)
•
Electrodeionization (EDI)
The service provider’s DeltaFlow* system is the primary make-up system design serving the TVA system. The DeltaFlow system combines three
membrane separation technologies: RO, Liqui-Cel*
GTM* and E-Cell* EDI into a continuous, reliable
ultrapure water treatment system. Moreover, the
DeltaFlow system can produce <5 ppb dissolved
oxygen by adding catalytic chemical deoxygenation
or multiple-pass GTM for nuclear plant make-up
specifications.
Kingston Make-Up System
The Kingston plant had a 17-year-old conventional
three-step ion exchange make-up system. Problems with the 300 gpm (68 m3/h) dual-train demineralizer included inconsistent regenerations and
effluent quality, resin fouling, hazardous regenerant
chemical leaks, and high operational and maintenance costs. Hot water was used to elevate the
anion resin bed temperature during caustic regeneration. Hot water supply problems almost caused
an explosion when the hot water tank overheated
and melted all lined piping in contact with the unit.
During the last year of operation, a leaking regenerant valve contaminated five (5) units with
caustic when both fail-safe conductivity shutdown
features malfunctioned.
typically varies between 200-300 ppm TDS, and
10-30 NTU. Effluent quality is typically <1 NTU.
The service provider’s design includes ion exchange
softening and activated carbon as pretreatment to
the DeltaFlow system. Ion exchange softening beds
provide media filtration to remove any trace suspended solids, and exchange divalent and trivalent
scale forming cations for sodium. The granular activated carbon beds provide polishing filtration and
dechlorination. This combination of pretreatment
steps allows the DeltaFlow system to produce
ultrapure water, and requires no chemical feeds.
The make-up system was fabricated and delivered
by the service company in self-enclosed equipment
housings. TVA requested this containerized design
to eliminate the need for a supplemental system
during the demolition of the bulk chemical storage
tanks and the demineralizer system. Containerized
equipment also offered TVA rapid start-up and
operation, and an easy transition phase between
the two systems. In the containerized design, all
electrical wiring and interconnecting piping were
prefabricated and tested at the service provider’s
facility. Upon arrival at the Kingston plant, TVA just
had to hook-up electrical feeds and connect the
external piping, and the system was ready for service. TVA selected a containerized equipment design at half of the outsourced make-up systems, the
balance being building enclosed.
Figure 5 illustrates the make-up water quality
improvement after commencement of the service
provider’s make-up system at Kingston Fossil Plant.
Results at Kingston
The 300 gpm (68 m3/h) DeltaFlow system began
service in August 1998. To meet the higher pretreatment requirement with RO systems, TVA
upgraded the existing inclined tube clarifiers to
increase performance and durability. The plastic
tubes were replaces with stainless steel inclined
tube settlers. The wood baffles and supports were
replaced with HDPE. An in-line turbidity analyzer
and level/flow indication instrumentation were
added to better monitor performance and maintain
effluent quality. The raw water to the clarifier is a
mixture of the Tennessee and Clinch rivers, which
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Figure 5: TVA, Kingston Fossil Make-up Quality
Conventional ion exchange is still required in the
production of “ultrapure” water. The current generation electrochemical demineralization technologies are not capable of consistently producing the
Page 7
make-up water quality required by high pressure
steam
generating
systems.
The
0.056
micromho/cm specific conductivity and <5 ppb silica (as SiO2) effluent quality is achieved by conventional mixed bed ion exchange polishing of the EDI
product water, with off-site chemical regeneration.
Footnotes
Conclusion
2. Miller, W.S., “Make-up Water Treatment by Service Contract,” 55th International Water Conference, Pittsburgh, PA, October 1994
On the eve of deregulation and with the growing
use of gas turbines to generate electricity, power
plant operators are challenged to develop and
implement methods to reduce costs and remain
competitive in the generation industry. In addition
to cost considerations for water treatment, a company may better position itself for the future by
evaluating the influence of current and future
wastewater discharge regulations on the proposed
treatment scheme. TVA identified hazardous
regenerant chemical use and wastewater discharge as potential operational and environmental
economic liabilities.
Water treatment service contracts can offer advantages to system suppliers and plant designers by
presenting alternatives to conventional water
treatment designs. Membrane technologies and offsite resin regeneration services can eliminate bulk
hazardous chemical storage tanks, transfer equipment, the maze of valve trees, and large waste
neutralization basins. All can translate into a
smaller real estate requirement and a less capitalintensive project.
1. Bartley, G.L., “Capital and Service Contract
Reverse Osmosis Systems at TVA’s Fossil
Plants,” 57th International Water Conference
Proceedings, Pittsburgh, PA, October 1996,
pp. 672-679.
3. Painter, J.C., “Benefits of Non-capital Make-up
Systems,” NUS Make-up Water Treatment
Seminar, Clearwater Beach, FL, June 1993.
4. Strauss, S.D., “Water Treatment,” Power, June
1993, pp. 17-112.
5. Ibid
6. Bartley, G.L., “Capital and Service Contract
Reverse Osmosis Systems at TVA’s Fossil
Plants,” 57th International Water Conference
Proceedings, Pittsburgh, PA, October 1996,
pp. 672-679.
7. Ibid.
The use of contract services for off-site condensate
polishing resin regeneration and make-up water
treatment allowed TVA to eliminate regenerant
chemical storage, handling, and wastewater discharge at all their fossil plants. This improved
water quality and economics, supported TVA’s corporate Environmental Leadership goal, and allowed
the utility to refocus resources on efficient power
production. Although no single approach provides
all the answers, outsourcing water treatment services can provide economic, operational, and environmental advantages to existing power plants.
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