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Boiler Technical Training At Reliance Industries Limited Hazira Manufacturing Division K S Rajan
RIL-Hazira/BWT-Technical Training GEWPT-- Conf GEWPT Confidenti idential al Material
February 26, 2008
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BOILER WATER TREATMENT
• • • • •
BASIC WATER CHEMISTRY BOILER DE DESCRIPTION OXY XYGE GEN N PI PITTTIN ING G & CON ONTTROL CONDENSATE TREATMENT INTE IN TERN RNAL AL TR TREA EATM TMEN ENT, T, CO COOR ORDI DINA NATE TED D pH/PO4 • STEAM PURITY • BOILER STORAGE • DISCUSSION, Q&A RIL-Hazira/BWT-Technical Training GEWPT-- Conf GEWPT Confidenti idential al Material
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BOILER WATER TREATMENT
• • • • •
BASIC WATER CHEMISTRY BOILER DE DESCRIPTION OXY XYGE GEN N PI PITTTIN ING G & CON ONTTROL CONDENSATE TREATMENT INTE IN TERN RNAL AL TR TREA EATM TMEN ENT, T, CO COOR ORDI DINA NATE TED D pH/PO4 • STEAM PURITY • BOILER STORAGE • DISCUSSION, Q&A RIL-Hazira/BWT-Technical Training GEWPT-- Conf GEWPT Confidenti idential al Material
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Basics & Interpretation of Water Analysis
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“The Basics”
• • • • • • • •
RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material
Hydrologic Cycle Properties of Water pH and Alkalinity Langelier Saturation Index Analytical Expressions Water Analysis/Deposit Analysis Corrosion and Deposition & Monitoring Chemical Feed
Properties of Water
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•Density - 1 kg/l @ 4 oC ; 0.998 kg/l @ ambient temperature and varies inversely with temperature •Boiling point = 100 oC and freezing point @ 0 oC •Viscosity ~ 1 cps at ambient temperature and varies inversely with temperature •Specific heat - 1 BTU/lb-deg F or 1 kcal/kg-deg C or 4.2 kJ/kgdeg C •Universal solvent - dissolves most substances to some extent
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Impurities found in Water
• 3 Categories • SUSPENDED SOLIDS (Silt)
• DISSOLVED SOLIDS (Minerals) • DISSOLVED GASES
• Where do these things come from? RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material
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Impurities found in Water
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•
Dissolved solids present as ions
•
Cations - Ions that carry net positive charges e.g. Calcium (Ca2+), Magnesium (Mg2+), Sodium (Na+), Iron (Fe2+), Aluminium (Al3+)
•
Anions - Ions that carry net negative charges e.g. Bicarbonates (HCO3-), Carbonates (CO32-), Sulfate (SO42-), Chlorides (Cl-), Oxides (O2-), Hydroxides (OH-)
RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material
Water Impurities
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Impurity
Concern
Removal
Suspended Solids Silt, Iron, Microbiogical
Fouling Erosion Underdeposit corrosion
Clarification Filtration
Dissolved Solids Minerals, Organics
Scaling Corrosion
Ion Exchange Reverse Osmosis Evaporation
Dissolved Gases O2, CO2, NH3
RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material
Pitting General Corrosion Corrosion products
Deaeration Steam Stripping
Dissolved Solids
Cations Temporary Hardness
Ca++
Anions
Mg++
Permanent Hardness
HCO3possibly OH- & CO3-Cl-
Na+ K+ NH4+
NO3-
F-
PO4 ---
SO4--
SiO2, possibly free CO2 Organic acids
Total Alkalinity
Mineral Acidity
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Dissolved Solids Commonly Found in Water
Cation
Anion
Calcium
Bicarbonate Sulfate
Ca(HCO3)2 CaSO4
Magnesium
Bicarbonate Sulfate
Mg(HCO3)2 MgSO4
Sodium
Bicarbonate Sulfate Chloride
NaHCO3 Na2SO4 NaCl
Silica
Oxide
SiO2
Iron
Bicarbonate Hydroxide Sulfate
Fe(HCO3)2 Fe(OH)3 FeSO4
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Chemical Name
Factors Affecting Solubility
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•Temperature - Most salts increases except for Ca and Mg Salts with increasing temperature
•Alkalinity - Most salt solubility increases with decreasing alkalinity with the exception of Silica
•pH - most salts solubility increases as the pH drops •Oxidation state - Fe and Mn salt solubility increases with decreasing oxidation state
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Impurities found in Water • Turbidity - suspended solids – silt, organic matters, precipitated salts • Color - suspended solids and dissolved solids • Dissolved gases e.g. CO2, O2, NH3, H2S • Organics - humus, vegetation, microorganisms
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Typical Water Analysis
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Parameter
Value
pH
7.3 150 0 20 15 10 20 15 5 0.05 1.5 12 <0.05 4 50 20 3 1
Conductivity μS/cm Alkalinity “P” as CaCO3, ppm Alkalinity “M” as CaCO3, ppm Sulfate as SO4, ppm Chloride as Cl, ppm Hardness, Total, as CaCO3, ppm Calcium Hardness, as CaCO3, ppm Magnesium Hardness, as CaCO3 ppm Copper, Total as Cu, ppm Iron, Total as Fe, ppm Sodium, as Na, ppm Phosphate, Total, as PO4, ppm Silica (reactive), as SiO2, ppm Turbidity, NTU TSS, ppm Color, Hazen RIL-Hazira/BWT-Technical Training TOC, as C, ppm GEWPT- Confidential Material
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Special Ions
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• pH •
•
Hydrogen, H+ Hydroxide, OH-
• Alkalinity • • •
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Bicarbonate, HCO3Carbonate, CO3-Hydroxide, OH-
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pH
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• • • •
RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material
Hydrogen Ion Concentration Logarithmic Scale pH = -log [H+] Unit change in log scale
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How Does pH Apply to Us? • pH < 7: Acidic (corrosion) • pH > 7: Alkaline (deposition)
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Alkalinity Relationships
•M-Alkalinity = Total – Titration to pH = 4.3 – Sum of: HCO3- + CO3- + OH•P-Alkalinity = OH- + 1/2 CO3– Titration to pH 8.3 •OH-Alkalinity = 2P - M or titration – Neutral barium chloride precipitates CO 3-
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Conductivity
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• Inverse of Resistance [mho] • Measure of concentration of ions in solution
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Types of Solubility
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Normal: Increases with Temperature • •
Table Salt (NaCl) Sugar
Retrograde: Decreases with Temperature • •
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Calcium Carbonate Calcium Phosphate
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How Do We Quantify What Is in the Water?
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Analytical Expressions
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• •
“Concentration” units of solute per unit of solvent: • PPM (parts per million) –
•
mg/l (milligrams per liter) –
•
RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material
parts of solute per million parts of solvent 1 gram solute/1,000,000 grams solvent PPB (Parts Per Billion) parts of solute per Billion parts of solvent
Analytical Expressions
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•“Mg as CaCO3” Magnesium expressed as its Equivalent weight in Calcium Carbonate 100 (MW CaCO3) = 4.1 24 (MW Mg)
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Analytical Expressions
• • • • • • •
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Different Conventions We use “ppm as CaCO3” ppm as substance factors Ca 50 2.5 Mg 20 4.1
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ppm as CaCO3 125 82
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Boiler Boiler Descriptions Descriptions
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FIRETUBE BOILERS ADVANTAGES High load swing capacity Ease of repair Low space requirement Self contained package Relatively low cost Ease of installation
DISADVANTAGES Low pressure Capacity limit Usually no superheater Usually no economizer Usually low efficiency One fuel at a time
FOUR-PASS FIRETUBE BOILER
WATERTUBE BOILERS
Typical Parts of a Water Tube Boiler Includes:
– – – – –
Economizer Steam drum Mud Drum Headers Boiler Bank • Downcomers - Risers • Waterwalls • Screen tubes • Arches • Floor tubes • Roof tubes – Superheater – Air Heater
WATERTUBE BOILERS RISERS SUPERHEATER
DOWNCOMERS STEAM DRUM
SCREEN TUBES
ECONOMIZER WATER WALLS
AIR HEATER
MUD DRUM
Coal
140-150 C
To stack
BOILER DESIGN
Lower Water Walls Header
Comparison - Watertube vs. Firetube: Water Tube
Fire Tube
Steam
Feedwater
Steam Drum
CBD
Risers
Flue Gases
Mud Drum
Downcomers IBD
Water
Flue Gases
WATERTUBE BOILERS ADVANTAGES Low to super critical pressure Virtually unlimited capacity Typically high efficiency Superheaters Economizers Multiple fuels Drum or once-through Package or field-erected
DISADVANTAGES High Cost Require Large Space Usually require higher quality feedwater Sensitive to low load operation
WATERTUBE BOILER: A-TYPE
Risers Steam Exit Drum
W B F
Downcomers
Burner
Flue Gas Path
Sidewall Problem Area
Steam Drum
D-Frame Package Boiler
Downcomers
Furnace Wall Tubes Risers
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Coal FiredMore Boiler Power.
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Infrastructure Power Utility Boiler Simplified Flow Diagram Water & Process Technologies
Hot Reheat
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HP Turbine HP SH Steam Sat Steam Condenser IP Turbine
LP Turbine
B&W Boiler
BD Cold Reheat LP Heaters Cond Polisher
HP Heaters BFW
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Deaerator
MB MU
CAUSE AND EFFECT DIAGRAM FOR BOILER PROBLEMS POOR pH CONTROL
OXYGEN PITTING POOR CHEMICAL FEED CONTROL
INADEQUATE BLOWDOWN CONTROL
OXYGEN IN-LEAKAGE
MECHANICAL DEAERATOR PERFORMANCE
DOWNTIME CORROSION
POOR BOILER FEEDWATER QUALITY
SCAVENGER UNDERFEED
CONDENSATE CONTAMINATION
DOWNTIME CORROSION
POOR EXTERNAL TREATMENT
BOILER CORROSION
POOR BOILER FEEDWATER QUALITY CONDENSATE CONTAMINATION POOR EXTERNAL TREATMENT INADEQUATE BLOWDOWN CONTROL
STRESSED AREA
CONCENTRATING MECHANISM
POOR CHEMICAL FEED CONTROL EMBRITTLING WATER CHARACTERISTICS
DEPOSITION
STRESS CORROSION CRACKING
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Boiler Calculations
FeedWater = Steam + Blowdown % Blowdown =
1 X 100 Cycles
FeedWater (kg/hr) = Steam Generation (kg/hr) 1 – (%blowdown) 100 FW= STM ( C ) C-1
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Determining Cycles of Concentration
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•Feedwater vs. Boiler Water analysis •BFW Cycles = [Boiler Conc.] / [FW Conc.] •
Cycles =
Neutralized Boiler Water Cond. (umhos at 25C) ___________________________________________ Feedwater Cond. (umhos at 25C)
•
Check via Chlorides, Silica
•
Do not use compounds that routinely precipitate (phosphate, hardness) or that are part of treatment (sulfite/sulfate)
•Demineralized or RO make-up – Tracer methods •
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Molybdate
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Steam, Feed Water & Blowdown Relationships
% Blowdown = 100 / FW Cycles •
% BD at 20 FW cycles = 100/20 = 5%
Feedwate Feed waterr = Stea Steam m X [Cycl [Cycles es / (Cycl (Cycles es –1)] •
RIL-Hazira/BWT-Technical Training GEWPT-- Conf GEWPT Confidenti idential al Material
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FW = 100 MM MM ppy steam steam X [20 / (20 – 1)] = 105.3
Feedwater = Steam Feedwater Steam + Blowdown Blowdown (105.3 3 – 100 100)) MM ppy = 5.3 MM MM • BD = FW – ST = (105. ppy
Feedwater Feed water = Make-up Make-up + Condensate Condensate
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Oxygen Control
• Deaeration • Chemical treatment
RIL-Hazira/BWT-Technical Training GEWPT-- Conf GEWPT Confidenti idential al Material
Corrosion of Iron by Oxygen
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O2 Fe(OH)3 Fe2+
OH-
O2
WATER ELECTRON FLOW
ANODE
CATHODE
ANODE REACTION Fe. = Fe++ 2e-
CATHODE REACTION 1/2 O2 + H2O + 2e- = 20H-
MECHANISM • •
RIL-Hazira/BWT-Technical Training GEWPT-- Conf GEWPT Confidenti idential al Material
Iron Is Oxidized on the Surface (Anode) - Metal Loss Oxygen Is Reduced (Cathode)
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Oxygen Corrosion
• Corrosion Rate Doubles With Every 10 C Increase in Water Temperature • Metal Loss is low • Localized attack • Pit Formation • Rapid Failure
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Rapid Perforation ~ Equipment Failure
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Oxygen Guidelines
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Organization
RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material
Dissolved O2 Level, ppb ASME
<7
TAPPI
<7
ABMA
NO RECOMMENDATION
EPRI
<5
DEAERATOR GUARANTEE
7
TYPICAL DEAERATOR O2 LEVELS
15 - 40
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Types of Oxygen Scavengers • Solid – Sodium Bisulfite – Sodium Sulfite • Non-Solids – Hydrazine – Hydroquinone – Diethylhydroxlamine (DEHA) – CARBOHYDRAZIDE – ASCORBIC ACID
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RECOMMENDED SULFITE CONTROL LIMITS
Residual (ppm SO3-) 30 - 60 10 - 20
Pressure < 40 bar 40 - 60 bar
ATTEMPERATION / DESUPERHEATING:
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NO
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Hydrazine
Reaction: N2H4 + O2 N2 + 2H2O Decomposition Reaction: 2N2H4 + HEAT + 2H2O 4NH3 + O2 Feedrates: 3 x (ppm O2 + Residual) Control Limits: 0.1 ppm Residual N2H4 at Economizer Inlet Attemperation / Desuperheating: Yes
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Hydrazine
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• Advantages: – Doesn’t contribute to TDS – True residual test • Disadvantages: – Poor reactivity with low temperature – Expensive compared to Sulfite – Suspect carcinogen – Requires special handling / feed equipment – Decomposes to NH3, which can lead to copper corrosion
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Organic O2 Scavengers
• Pressure > 900 psig (60 bar) • BFW used for superheat attemperation • Condensing turbine present • High-Purity Makeup (Demin./RO) • Coordinated PO4 / pH control
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HYDROQUINONE
OH REACTION: C6H6O2 + 1/2O2
CONTROL LIMITS: DISSOLVED OXYGEN TEST IRON REDUCTION TEST
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H2O + C6H4O2
OH
HYDROQUINONE
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ADVANTAGES
• • • • • •
DOES NOT CONTRIBUTE TO TDS FASTEST ORGANIC OXYGEN SCAVENGER REQUIRES NO SPECIAL HANDLING EXCELLENT FOR WET LAY-UP AVOIDS SULFUR CATALYST POISON NOT A LISTED CARCINOGENIC
O
OH
+ O2 = RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material
OH
O
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Carbohydrazide
O REACTION: N4H6CO + O2
2 N2
DECOMPOSITION REACTION: N4H6CO + H2O + HEAT
2N2H4 + CO2
2N2H4 + HEAT + 2H2O
4NH3
+ O2
CORTROL-OS-5613 RESIDUAL(0.3-0.5 ppm product)
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3 H 2 N - C
2 N H 3
+ 3H2O + CO2
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Carbohydrazide Advantages • Low/no cation conductivity contribution – Does not form LMW organic acids – CO2 contribute to non degassed cationic conductivity • Well-accepted in Industry • Much safer than hydrazine RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material
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Variables Influencing Scavenger Reaction
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• • • •
RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material
Time Temperature pH Catalyst
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pH and Temperature Recommendations
OXYGEN SCAVENGER
MINIMUM TEMP*
MINIMUM pH*
SULFITES
80 OF (27 C)
>8.5
HYDRAZINE
190 OF (88 C)
>8.5
HYDROQUINONE (HQ)
80 OF (27 C)
>8.5
HYDROXYLAMINES (HA)
>200 OF (> 93 C)
>8.5
180 OF (82 C)
>8.5
>200 oF(> 93 C)
>8.5
ASCORBIC ACID CARBOHYDRAZIDE
*FOR EFFICIENT OXYGEN SCAVENGING PERFORMANCE
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Monitoring
Ideal Point
1
ECONOMIZER 2
1) 2)
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Primary sample point for oxygen testing Sample point necessary for deaerator studies and for troubleshooting oxygen intrusion through the pump
MONITORING
• • • • •
pH Conductivity Hardness, silica Oxygen Corrosion – metals analysis – corrosion coupons
Millipore Iron Testing
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Feed Water and Condensate System Treatment • Ammonia • Amines • Condensate polishing
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Condensate Treatment In The Condensate: • Carbon Dioxide CO2 + H2O H2CO3
H2CO3 H+ + HCO3-
pH DECREASES
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Feedwater Alkalinity Is a Source of CO2 in Condensate
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IN THE BOILER:
2HCO3CO3=
CO3= + H20 + CO2 CO2 + 2OH-
STEAM CO2
FEEDWATER HCO3CO3=
OH-
BLOWDOWN RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material
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Copper Alloys and Carbon Steel vs pH
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CARBON STEEL CORROSION RATE COPPER
7
8
9 pH
RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material
10
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Fundamental Amine Characteristics • Distribution Ratio • Neutralizing Capacity • Basicity • Thermal Stability
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NEUTRALIZING AMINES
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R - NH3+ + HCO3-
R - NH2 + H2CO3
R - NH3+ + OH-
R - NH2 + H2O
10
H p , E T A S N E D N O C
9
8
7
6
5
0
2
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4
6 8 10 AMINE FEED (ppm)
12
14
16
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BASICITY
Neutralizing Basicity Constant Morpholine Ammonia Ethanolamine DEAE MOPA Cyclohexylamine
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2 18 32 66 126 440
DISTRIBUTION RATIOS
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DR = Concentration in steam Concentration in liquid
VAPOR LIQUID HIGH DISTRIBUTION RATIO RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material
LOW DISTRIBUTION RATIO
DISTRIBUTION RATIOS
AMINE AMMONIA CYCLOHEXYLAMINE DEAE MOPA MORPHOLINE ETHANOLAMINE DIAMINE CONTAMINANTS CO2
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0 PSIG 10 4.0 1.7 1.0 0.4 0.07 0.45 5400
DR 200 PSIG 1000 PSIG 7.1 3.6 16.0 9.3 4.5 3.4 2.4 2.5 1.6 1.0 0.15 0.29 1.9 2.7 500
100
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Boiler Internal Treatment & Steam Purity • Coordinated PO4 /pH • Steam purity
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Deposit Formation
• • • • •
Deposition rate increases with heat flux (Btu/Ft2) Reduces Heat Transfer Increases tube wall temperature Induces corrosion Ultimately - Tube failure
Effect of Deposition on Heat Transfer Tube Metal
Insulating Scale
800°F Fireside Combustion Gases
600°F Fireside 500°F Waterside
Scaled Tube Surface
500°F Waterside
Clean Tube Surface
Cause and Effect Diagram for Boiler Deposition Infrastructure Water & Process Technologies
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Monitoring Tools 1. Monitor NaZ Performance: 2. Monitoring Boiler Feedwater/ Condensate Hardness 3. On-Line Hardness Analyzers 4. Equipment Inspections 5. Routine Blowdown Testing 6. Data Tracking
Monitoring Tools 1. Boiler Feedwater/ Condensate Iron Monitoring 2. Turbidity Monitoring 3. Equipment Inspections
Hardness Salts
Iron
Intermittent Contamination
Intermittent Contamination
Condensate Hardness Contamination
Condensate Corrosion
Poor NaZ Performance Chemical Underfeed Poor Blowdown Control
Chemical Underfeed Poor Blowdown Control Poor Storage Practices Deposition Fouling
Poor Chemical Feed Control Condensate Hydrocarbon Contamination
High Boiler Silica Poor Separation Equipment Performance Rapid Load Swings Hydrocarbon Contamination Poor Blowdown Control
Hydrocarbon Monitoring Tools 1. On-Line Total Analyzer 2. Boiler Feedwater Inspection 3. Equipment Inspections
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Header Pressure Swings
Superheater/Turbine Fouling Monitoring Tools 1. Steam Purity Monitoring 2. Routine Boiler Testing 3. On-Line Sodium Analyzer 4. Equipment Inspections 5. Data Tracking
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Coordinated Phosphate/pH Programs
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Used Primarily in high pressure boilers to protect against caustic gouging Applicable for lower pressure boiler systems on demin quality makeup Sodium (caustic) is primary feedwater contaminant Iron may also be a problem polymers used for iron control
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Coordinated PO4/pH Boiler Treatment • To control boiler water pH...... • ......Create a buffer system between PO4 and NaOH
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Under-Deposit Corrosion
High or Low Boiler Water pH Corrodes Boiler Steel
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RELATIVE CORROSIVE ATTACK
8.5 pH
12.7 pH SAFE RANGE
1
2
3
4
5
6
7
8
pH RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material
9
10 11 12 13 14
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Na: PO4 RATIO OUT OF CONTROL EXCESS “SODIUM LEAKAGE”
Na2 HPO4 + 2NaOH
Na3PO4 + NaOH + H2O
Low DSP Fed
“Free Caustic”
4Na + 1PO4 Na:PO4 = 4:1
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PREVENTING CAUSTIC CONCENTRATION
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NaOH + Na2HPO4 Caustic
Disodium Phosphate
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Na3PO4 + H2O Trisodium Phosphate
Water
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Coordinated Phosphate/pH Control
2Na2 HPO4 + 2NaOH “Exact” DSP Fed 6Na + 2PO4 Na:PO4 = 3:1
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2Na3PO4 + 2H2O
Under-Deposit Neutralization
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10.8 10.6
M A X I M U M B O U N D A R Y 3 .0 :1 M O L A R R A T I O ` ` F r e e '' C a u s t i c
10.4
Region
10.2
2.8:1 Na/PO 4
Control Area
< 90 0 p si
10.0 2.7:1 Na/PO 4
9 .8
pH AT 25C
Control Area
`` C a p t i v e ''
9 0 1 -1 5 00 p s i
Alkalinity Region
9 .6 9 .4
2.6:1 Na/PO 4 Control Area
1 5 01 -2 0 00 p s i
9 .0 8 .8 8 .6
TRI-SODIUM PHOSPHATE
CAUSTIC
9 .2
Control Area Vector 2 0 01 -2 5 00 p s i CONTROL BOUNDARY Control
2.2:1 Na/PO 4 M O L A R R A T IO
Control Area > 26 00 p si
8 .4 8 .2 1 .0
DI-SODIUM PHOSPHATE
Diagram
BLOW DOW N
M O N O -S O D IU M PHOSPHATE
CONTRO L AREA 2 50 1 -2 60 0 p s i 2
3
4
5 6
7
8
10
15
20
30
p p m O r th o p h o s p h a te , as P O 4
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40
50
60
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Caustic-Phosphate Equilibrium
Caustic
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Tri-sodium PO4
Di-sodium PO4 Blowdown Mono-sodium PO4
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Reality Check Your 90 bar boiler has a pH 9.5 and PO4 of 30 ppm. Boiler PO4 control range is 10 - 20 ppm How should we respond?
[A]
Reality Check Your readings for this 100 bar boiler are pH 10.2 and PO4 of 6. PO4 control range is 4 - 8 ppm. What actions will put you back into control?
[A]
Acid Phosphate Corrosion
Acid PO4 corrosion potential exists when boiler water Na/PO4 ratio is less than 2.3
Sodium PO4 (Di or Mono) can react with Magnetite or Iron to form Maricite (NaFePO4) under high temperature (>300 C)
Steam Purity
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Importance of Steam Purity
Protect Capital Investments, such as:
– Superheaters – Turbines – Steam lines and valves
Maintain Production
Prevent Process Contamination
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Definitions
• Steam Purity Solid, liquid or vaporous contamination in the steam • Steam Quality A measure of the moisture in the steam
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Steam Purity Guidelines
• Turbine manufacturer (ppb levels) • Boiler manufacturer (ppm levels) • Industry professional organizations • Operations
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Turbine Manufacturers’ Steam Purity Limits
PARAMETER
General Electric NORMAL
100 HR.
24 HR.
Westing house NORMAL
2 WEEK
24 HR.
Allis Chalmers NORMAL
Cation Cond. uS/cm Sodium, ppb
0.2
0.5
1
0.3
0.3-0.5
0.5-1.1
0.1
3
6
10
5
5-10
10-20
10
Chloride, ppb
A
A
A
5
5-10
10-20
10
Silica, ppb
A
A
A
10
10-20
20-50
10
Iron, ppb
A
A
A
20
5
Copper, ppb
A
A
A
2
1
Oxygen, ppb
A
A
A
10
A - Governed by requirements of the steam-generator manufactureer
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10-30
30-100
5
Steam Turbine - Problems • Deposition
– Deposit thickness 0.1 mm reduces stage efficiency by 3% • Surface Roughness
– Affects flow passage width – Reduce stage efficiency • LP Blade corrosion
– Stress corrosion cracking (NaOH, Cl) – Pitting – Erosion
Industrial Steam Turbines Typical Sources of Impurities Chemical Cleaning
Makeup Water
Air In-Leakage
Demineralizers Water and Steam
Condenser Leaks
Corrosion Products
Water Treatment Chemicals
Process Chemicals
STEAM PURITY
Steam Purity vs Steam Quality • Steam purity is the solid, liquid, or vaporous contamination in the steam • Steam quality is the measurement of moisture in steam
Steam Purity Guidelines • Turbine & Boiler Manufacturers • Industry Professional Organizations
– (ASME, ABMA, EPRI, VGB, BS ) • Boiler Manufacturers • Operations
Steam Purity Guidelines Normal Operation
Parameter
ABB
GE
Na,
ppb
< 10
<20
< 10
< 10
SiO2,
ppb
< 20
< 20
< 20
< 15
Total Fe, ppb
< 20
< 20
<5
Cu,
ppb
<3
<2
Cl,
ppb
Cationic Cond. us/cm
<0.2
< 0.2
Westinghouse Mitsubishi
< 15
<2
< 0.3
< 0.2
Steam Purity Guidelines Abnormal Operation (Westinghouse) * Time refers to continuous time in the range and also to total time in a 12-month period in the range
Parameter
2-week *
24-Hour *
Immediate Shut Down
Cation Cond. us/cm Na, ppb
0.3 - 0.5
0.5 - 1.0
> 1.0
10 - 20
20 - 35
> 35
SiO 2, ppb
20 - 40
40 - 80
> 80
Cl, ppb
15 -30
30 - 50
> 50
SO 4, ppb
15 -30
30 - 50
> 50
CARRYOVER: MECHANICAL CAUSES
• STEAM SEPARATION EQUIPMENT • STEAM DRUM LEVEL • STEAM LOAD • OVERFIRING
CARRYOVER: CHEMICAL CAUSES
• FOAMING
–TDS –Alkalinity – Organ Organics/ ics/ Polymer Polymer Overfeed Overfeeding ing –Antifoam • SELECT SELECTIVE IVE VAPO VAPOROU ROUS S CARRYO CARRYOVER VER (GOV (GOVERN ERNED ED BY DRUM DRUM pH, PRESSURE AND TEMPERATURE
–Silica – Ot Othe hers rs - Cl Cl,, SO SO4, Fe
ATTEMPERATION WATER
• FEEDWATER
–Quality of Feed water –Chemical Treatment • SW SWEE EETT WATE WATER R COND CONDEN ENSE SER R
–Source of Coolant –Purity of Steam Source • CONDENSATE
MONITORING STEAM PURITY
SODIUM • On Line Analyzer • Isokinetic Sampling • Bottle Study (Na free bottles)
• Saturated Steam
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Boiler Storage • Most oxygen corrosion occurs or is initiated when boiler is off-line (wet storage) • Key to Success - Alkaline & oxygen-free during wet storage
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Boiler Storage
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• Dry Storage with a desiccant is recommended for long-term storage • What constitutes ‘long-term’? – Off-season storage – Rule-of-thumb: Normally recommend dry storage if lay-up will be >1 month and boiler will not be needed on short notice
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Boiler Storage
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• Wet storage is recommended when: – Boiler is required for emergency stand-by or on short notice – Capacity required to meet peak demand – Unit will be out-of-service for < 1 month
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Wet Storage Methods 1. Volatile Chemicals 2. Sulfite & Caustic 3. Cascade lay-up / Hot standby 4. Dry lay-up with desiccant
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General guidelines for wet storage with chemicals
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• Add chemicals to fill water as it is pumped into boiler • Fire boiler moderately after chemical addition to circulate & distribute or utilize external circulation pump – Always follow boiler manufacturers recommendations for firing the boiler • Adjust pH/alkalinity with amine or caustic consistent with the lay-up chemical being used.
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General guidelines for wet storage of high-pressure boilers with chemicals
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• Weekly testing during wet storage – Measure pH/Alkalinity – Test dissolved oxygen and/or scavenger residual – Maintain dissolved oxygen level below 10 ppb – Supplement scavenger/amine as required • Preventing oxygen ingress during storage: – Connect surge tank (drum) filled with lay-up solution to upper vent – Alternative - 5 psig (0.34 bar) nitrogen ‘cap’ RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material
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Volatile Chemicals • Required when: – Above 900 psig (60 bar) – Non-drainable superheaters – Turbines – High-purity make-up • Sulfite is NOT suitable
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Volatile Chemicals
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• Acceptable water for preparation of highpressure boiler lay-up solutions: – Good-quality demineralized H2O – Good quality condensate (no solids) – No softened-quality, RO or raw water with appreciable TDS • Add chemicals to fill water as it is pumped into boiler
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Suitable volatile oxygen scavengers
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• Hydroquinone – Fastest reaction with oxygen at ambient temp – Must use neutralizing amine with HQ – Important - Amine MUST be compatible with HQ (or will develop sludge): • Hydroxylamines – Most volatile & compatible with amines
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Suitable volatile oxygen scavengers
• Hydrazine - 200 ppm as N2H4 – Excellent passivator at > 200 ppm as N2H4, BUT: – Not recommended - Safety hazard! – Amine is not typically required • Ascorbic acid - Not recommended: – Poor thermal stability – Acidic decomposition products – Non-volatile
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Volatile Chemicals
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• Special lay-up product - CorTrol OS7700 • HQ plus special low-volatility amine package • Avoids low pH excursions on re-start • Feedrate: 2000 ppm product – 4000 ppm in new systems (nonpassivated) – Maintain pH above 10.5 throughout
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Dry Lay-up with Desiccant (Long-term storage)
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• Drain boiler • Hot air/heat to remove all moisture • Use desiccant (with color indicator) – Silica gel – Quick lime – Activated alumina
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PRESENT TREATMENT PROGRAM AT HAZIRA
• CORTROL-5613-OXYGEN SCAVENGER – FEED RATE 0.5-1.0 PPM – RESIDUAL MONITORING. • STEAMATE-NA8590 – CONDENSATE TREATMENT – LOW DR AMINE • TRI SODIUM PHOSPHATE – FOR pH/PO4 coordination • AMMONIA – FEED WATER & STEAM pH CONTROL
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