CASE HISTORY
solenis.com
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Power Generation
BWT-PG-CH-N460-02.14
FAC Mitigation at Combined Cycle Power Plant Reduces Iron
Transport by 50 Percent
Amercor™ 8780 Corrosion Inhibitor
Customer Overview:
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Segment:
Product(s):
Location:
Power Generation
Electricity
Southeast United States
Application Overview:
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Type:
Equipment:
Boiler Water Treatment
2 Multiple Drum Heat Recovery
Steam Generators (HRSG)
Capacity:
14,520,000 pounds per day
Other:
Large 550 MW standard 2 x 1
configuration, combined cycle power plant
operated by a large independent power producer.
The HP drum pressure is 1800 psig.
Existing Treatment:
The plant had been using a blend of aqua ammonia
and monoethanolamine (MEA) in accordance with a
corporate mandate. However since converting to this
regime, the plant continued to experience two phase
flow accelerated corrosion (FAC) in both LP drums.
Principle variables affecting FAC were presented to
plant management with the key focus on pH elevation
(see Figure 1).
Problem Summary:
To achieve proper pH elevation of the HRSG feed
water using the ammonia/MEA blend required twice
the typical feed rate.
In order to evaluate any chemistry changes, Solenis
offered to monitor iron transport with the Sentry*
Corrosion Products Sampler. Two units were installed
(one for each HRSG) and sampling began with the
following results:
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Iron at steady operation showed 0.5 to 0.6 ppb
Iron at cycling operation showed 1 to 3 ppb
It was determined that the ammonia/MEA blend was
not adequate in raising the feedwater pH to desired pH
ranges. As an alternative, a blended product of
cyclohexylamine and Methoxypropylamine (MOPA)
was selected and the trial was initiated with a strong
rise in feed water pH. However, after a few days, the
pH in both Intermediate Pressure (IP) drums fell to <
9.0.
Customer Objectives:
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FAC mitigation
Elevated feedwater and drum pH
Reduced iron transport
Lower cation conductivity values
Reduced chemical usage and cost
Solenis Solution:
Laboratory studies confirmed that MOPA yields a
lower pH depression from thermal breakdown than
cyclohexylamine and has a lower distribution ratio than
cyclohexylamine.
By 500 psig MOPA had started breaking down to into
organic acids resulting in a drop in IP drum pH values.
Figure 1 – pH versus metal wear rate
MOPA had now been evaluated and deemed
unacceptable due to the IP drum pH depression
while ammonia didn’t have enough basicity to raise pH
effectively. More discussion and review of technical
data led Solenis to further evaluate the affect of
cyclohexylamine.
All statements, information and data presented herein are believed to be accurate and reliable, but are not to be taken as a guarantee, an express warranty, or an implied warranty of merchantability or fitness for a particular purpose, or representation, express or
implied, for which Solenis International, L.P. and its affiliates and subsidiaries assume legal responsibility. ® Registered trademark, Solenis or its subsidiaries, registered in various countries. ™Trademark, Solenis or its subsidiaries, registered in various countries.
*Trademark owned by a third party. © 2014, Solenis.
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Amine content data calculated during previous trials
suggested that cyclohexylamine and MEA would yield
the desired pH in feedwater without the organic acid
buildup in the IP drums. Amercor 8780 corrosion
inhibitor, a blend of cyclohexylamine and MEA was
selected as the next trial chemistry which started very
well with a strong rise in feedwater pH to 9.9.
Condensate pH ( 9.6 - 10.0 )
10
(NH3/MEA)
(MOPA/CHA)
9.9
Amercor 8780
(CHA/MEA)
NH3/MEA &
MOPA/CHA
@ 4:1 ratio
NH3/MEA @
Old pH settings
9.8
9.7
9.6
Dosage was approximately 6 to 8 gpd initially and over
the next several days, the required dosage to maintain
the 9.8 pH was 10 to 12 gpd.
All drum pH values were stable and steady at 9.6
and the LP steam pH rose to 10.4 (see Figures 2 and
3).
9.5
9.4
pH Before Chemical Feed
Figure 2 – Condensate pH before and after
chemical feed
Customer Benefits:
Conclusion:
During the outage, inspections revealed there had
been some improvement to the metal surfaces in the
LP drums. The visible areas of two-phase FAC had
been reduced with surfaces appearing dull and not
shiny as in previous inspections. The hotwell looked
much better than the previous inspection and was no
longer bright red as before.
Organic acids appeared to be concentrating in the
kettle boilers and creating a higher demand for the
Amercor 8780 corrosion inhibitor, so
recommendations were made to increase the
blowdown on the kettle boilers to reduce organic acid
accumulation and reduce Amercor 8780 feedrates.
The increased blowdown worked well and cation
conductivity dropped to ~ 2 uS/cm (see Figure 4) while
pH remained at 9.8 in the feedwater. The plant was
able to reduce the chemical costs by 54% with annual
savings of $75,000.
pH Comparison
10.4
10.2
10
9.8
9.6
9.4
9.2
9
8.8
Amercor
NH3/MEAKB
Amercor 8780
Figure 3 – Steam Cycle pH Comparison
Condensate Cation Conductivity (< 2 uS/cm )
6
Conductivity (uS/cm)
The Amercor 8780 corrosion inhibitor trial continued to
run until the next outage. Iron transport data indicated
approximately 50% reduction. Iron throw for steady
operations was 0.18 to 0.3 ppb iron and iron throw for
cycling operations was 0.5 to 1.0 ppb iron.
pH After Chemical Feed
NH3/MEA &
MOPA/CHA
@ 4:1 ratio
5
Amercor 8780
(CHA / MEA)
(MOPA /CHA)
4
3
2
1
(NH3/MEA)
NH3/MEA @
Old pH settings
Increased Blowdown
on Kettle Boilers to
Reduce organic acids
0
Figure 4 – Kettle Boiler Blowdown Reduces Cation
Conductivity