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Thailand Power Workshop Grouping
Bangkok office
29 & 30-Mar-2012
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Executive Summary
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Boiler System: Found the problem of Hydrogen damage issue. The root-cause was
come from condenser in-leakage issue from cooling part.
Solution
Review the chemical treatment program to effective control corrosionin system with Nalcos product.
Implement @T ORP on BFW to monitor the .
Cooling System:
High chloride issue in cooling system anytime.
Induce to face the stress corrosion cracking (SCC) on SS304condenser tube.
Solution
Review the chemical treatment program to effective microbial and alsocontrol chloride in system with Nalcos product.
Implement 3DTRASAR for cooling system.
Implement the condenser performance monitoring to ensure thetreatment program.
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General Information
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June 2011:Condenser in-leakage issue
Nov 2011:Low pH in BFW
Dec 2011:T/A to fix the condenser
Jan 2012:Normal run
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Problem analysis forBoiler system
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Speed
Governor
Variable Loading
HP Steam
Turbine
ValveShaft speed
Generator
Low pressure
steam
Hot
well
To boiler as feed water
Cooling tower
(Operating range 40-50 MW)
Condensate Return
DEAERATOR
HP Boiler LP Boiler
LP Steam
MB(Demin
MU)
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Boiler System
1 unit CFB Boiler
HP = 70 bar, 130 tons/hrConsisting of Economizer, Boiler, Superheater #1 and #2Deaerator
2 bar, 115-118 C, DO
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Important Issue
7
Boiler System
The plant experience with 2 (two) tube failures in December 2011.The failures were occurred in the water wall tubes about 5 m above theburner as showing in the picture below
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Hydrogen Damage
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The main problem with this failure is
that it gets spread across the waterwall tubes in totally an unpredictableway. Hence to find out the regionsaffected in the water wall bycondenser leakage, exhaustive specialprobe ultrasonic testing is required.
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Characteristics of Hydrogen Damage, Caustic Gouging andAcid Phosphate Corrosion
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Determine the root cause
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Major Root Cause Influence Confirmation Remark
Influence of excessive deposits Yes Deposit in steam drum (Boilerinspection May & Sep 2011)
Heavy deposition in sampling tube(Sep 2011)
Flow disruption: deposits, DNB,bend/sharp changes in tube direction,
locally high heat transfer, etc.
Yes Flow disruption only influence bydeposition
Influence of acidic contamination Yes pH of boiler drop to ~8.5 on May2011
Condenser leak-minor but occurredover an extend period
Yes pH of boiler dropped to ~8.4
Hardness in condensate went upto >0.5 ppm
Chloride concentration in HP
evap. went up >10 ppm
Water treatment plant up set leading tolow pH condition
No
Error in chemical cleaning process No No chemical cleaning conducted in2011
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BFW data trend
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8
8.2
8.4
8.6
8.89
9.2
11/2/2011
11/4/2011
11/6/2011
11/8/2011
1
1/10/2011
1
1/12/2011
1
1/14/2011
1
1/16/2011
1
1/18/2011
1
1/20/2011
1
1/22/2011
1
1/24/2011
1
1/26/2011
1
1/28/2011
1
1/30/2011
pH 8.5-9.2
pH 8.5-9.2
7.37.47.57.67.77.87.98.08.1
8.2
Conductivity
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Solution for Boiler system
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Immediate Solution
Isolate the condenser and plug all the leaking tubesand tubes with high depth wastage. Ensure there is nocooling water in-leakage by checking condensatequality (cation conductivity, hardness, chloride; etc)
Selective tube sampling for deposit measurement.Inspection using fiber optic (boroscope) can provideuseful information
Tube replacement for all tubing with hydrogen damage
and/or significant wall loss be replaced Check the efficacy of chemical cleaning
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Long Term Solution
Chemical cleaning
Proper chemical cleaning method/procedure
Prevent condenser in-leakage by improving integrity ofsurface condenser
Install on-line instrumentation to improve condenserleakage detection capability and cycle chemistry control
On-line cationic conductivity @CPD and outlet DA
DO meter @CPD and outlet DA
@Temp. ORP @ CPD/Inlet DEA and Outlet DA (optional)
Develop specific cycle chemistry targets, action levels andshutdown policies to maintain good HRSG cleanliness.
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Problem analysis forCooling system
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Open Cooling Water
RR = 6,000 M3/hr, HV = 1,000 M35 cell cross flow cooling tower with high efficiency fillTemperature Supply: 34 0CTemperature Return: 42 0C
Pipe: carbon steelCondenser
DT cooling water (design) = 8 0CTubes: SS 304Tubes Sheet: CS with epoxy coating
Lube Oil CoolersServed by open cooling water systemTubes: Cu:Ni = 90:10Tubes Sheet: CS with epoxy coating
Air CoolersServed by open cooling water systemTubes: Cu:Ni = 90:10Sheet: carbon steel coated with epoxy
Make-up water : clarified water
Source: river waterPretreatment: clarifier filter raw water tankcooling tower
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Important Issue
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Cooling Water System
There were condenser tube leak event occurred in the surface condenser in year 2011. The tubefailure occurred on June 2011, 5 tubes were cracked and leaked cause very high conductivity ofcondensate and low pH of boiler water (
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Nalco 3DTRASAR Optimizer
The cooling water quality at 6 cycle with no NaOCl
were not aggressive for Stainless 304
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When we run simulation program with NaOCl to control FRC0.2-0.5 ppm.
Higher chloride in cooling water will increase potential for stainlesscorrosion
From above snapshot we found there are issue of SS-304 corrosion thatmay be the root cause for this issue that make the penalty from unplanshutdown for 2 day around (3Bahtx20kwx1000x24hrx2day = 2.88 MB/time)
Nalco 3DTRASAR Optimizer
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Water Quality MU vs CW
Trend of Make up & cooling water quality seem stable, so the problem may behidden such as- not matching treatment program,- not matching control target
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Solution for Cooling system
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To prevent stainless corrosion in condenser and H2 damage in Boiler tubeWe recommend follow.-
1. Replace the oxidizing biocide form chloride to bromine base2. Replace treatment program
3. Use automation system control feeding system to increase systemreliability
4. Replace treatment program for more reliability5. Use automation system to monitor and control feeding system in Boiler
system
SOLUTION
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1. Replace the oxidizing biocide form chloride to bromine base
To prevent SS-304 corrosion, we recommend to use stabilize bromine foroxidizing biocide that will not increase chloride in water.
SOLUTION
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NALCO TREATMENT
SOLUTION
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Nalco 3DTRASAR Optimizer
With Nalco solution, we can run cooling system at 7 cyclewithout SS-304 corrosion or scale from Calcium Phosphate
All field aregreen
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Summary of Commercial part
C i l
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Commercial part
Units Price per Unit
Kg/Year 6.00
Kg/Year 165.00
Kg/Year 155.00
Kg/Year 198.00
Kg/Year 113.00Kg/Year 246.00
Kg/Year 81.00
Total Cont/Year
Total Treatment Costs 932,912.0
3,639,709.7
Internal Treatment BT-3000 4 Continuous Feed 5,616.0 454,896.0
Boiler System
Oxygen Scavenger Eliminox 0.5 Continuous Feed 562.0 63,506.0Condensate Treatment N-356 1.5 Continuous Feed 1,685.0 414,510.0
Product Category or
Control Parame ter
Scale Inhibitor
pH
Cycles of Concentration
Cooling System
TRASARMild Steel Corrosion Inhibitor
Oxidizing Biocide
Product Number or
Additive
3DT104
H2SO4
Control Method
Tag Polymer
Dosage or
Control Set
Point
7.0 3D Scale Control
31
7.6
0 Timer Control
253DT129
ST-70 1,717,567.0
3,245
2,649
8,675
Annual Cost
410,643.8
43,138.1
Annual Usage
7,190Automatic
535,448.8
2,706,797.7Total Treatment Costs
1) Chemical 303,309.14 Bht/m
2) Equipment rental
-3DTRASAR for CW + 4 pump + Solenoid valve 15,000 Bht/m-3DTfB (CONTROLLER & NCSM) 33,600 Bht/m
Total Treatment Cost 351,909 Bht/m4,222,909 Bht/Y
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Commercial part
3DTRASAR Value Package
38
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Workshop grouping
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