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Kraft Recovery CourseKraft Recovery Course

Recovery BoilerRecovery BoilerWater TreatmentWater Treatment

JanuaryJanuary20082008

Presented ByPresented By

Sheppard T. PowellAssociates, LLC

Baltimore Marylandwww.stpa.com

Presentation FormatPresentation Format

Objectives Of Treatment ProgramSteam/Water Cycle: Basic ComponentsTop Routine Chemistry ParametersSummary

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Objectives Of Treatment ProgramObjectives Of Treatment Program

00Turbines

00Superheaters

0 or MinorMinorBoiler

Minor--Feedwater System

Minor--Condensate System

CorrosionDepositComponent

Boiler Deposit ExampleBoiler Deposit Example

Thick Nose Tube Deposits of Copper and Copper Oxides Over Mixed Iron Oxide, Hardness Phosphate and Carbon

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Boiler Blistering ExampleBoiler Blistering Example

Boiler Corrosion ExampleBoiler Corrosion Example

Deposits After Brushing

Under-Deposit Corrosion

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Turbine Deposits ExampleTurbine Deposits Example

Superheater Corrosion ExampleSuperheater Corrosion Example

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Steam/Water Cycle DiagramSteam/Water Cycle Diagram

S

S

FeedwaterHeater(s)

DeaeratorAnd Storage

Steam

Steam

Vent

Desuper-heatingWater

MakeupStorage

Blowdown/MakeupHeat Exchanger

CondensateStorage

Mill Condensate(s)

TreatedMakeup

S

S

SS

S

S

S

S

S

S

S

Usually Operated As A Grab Sample Point

CondensateFilter/Polisher

System

NaCCNaCC

pHSC

pHSCNaDOSiO2

NaCC

SC

SC

SCSiO2Na

(For Each)

Desup.Water

SweetwaterCondenser

FW OutFW In

TUBoiler

QuestionsQuestions

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Specific ConductivitySpecific Conductivity

Total Conductive Solids (Salts, Acids, Alkalis)High Levels Can Cause Foaming and/or CorrosionUnits: Usually µS/cmMicromho (µmho/cm) = Microsiemen (µS/cm)Millimho (mmho/cm) = Millisiemen (mS/cm)1 mS/cm = 1000 µS/cm (Beware of auto-switching ranges on meter!)

Specific ConductivitySpecific Conductivity

(a) Much Higher For Low Pressure Boilers On Softened Makeup

3 to 5 × PO420 – 150 (a)Boiler Water

Amine Feed2.0 – 6.0Condensate & Feedwater

NaOH Leakage0.05 – 5.0Demineralized Water

Main SourceNormal Values, µS/cmSample

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Example of Amine Blend Effect on ConductivityExample of Amine Blend Effect on Conductivity

0 1 2 3 4 5 6 7 8 9 10Volume of Amine Blend, ppm

Spec

ific C

ondu

ct ivit

y,µS

/cm

12

10

8

6

4

2

0

Trial A - Change in SC(33.9 - 35.7°C)Trial B - Change in SC(34.0 - 36.3°C)

pH (Relative Acidity and Alkalinity)pH (Relative Acidity and Alkalinity)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14Neutral

106 105 104 103 102 10 1 1 10 102 103 104 105 106

Acid Units Base Units

pHpH

5% Sulfuric AcidLemon Juice

Vinegar

DemineralizedWater

Condensate/FeedwaterBoiler WaterHousehold Ammonia

4% Caustic Soda

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Example of Amine Blend Effect on pHExample of Amine Blend Effect on pH

Volume of Amine Blend, ppm1 2 3 4 5 6 7 8 9 10

pH9.4

9.2

9.0

8.8

8.6

8.4

8.2

Trial A - pH (33.9 - 35.7°C)Trial B - pH (34.0 - 36.3°C)

Effect of pH on Copper TransportEffect of pH on Copper Transport

1.0

10.0

50.0

0.27.0 8.0 9.0 10.0

pH

70Cu/30Ni90Cu/10NiCo

pper

C or ro

sion

Pro d

uctR

elea

se, g

/ mY e

ar2

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Dissolved OxygenDissolved Oxygen

Oxygen as O2 (from air) dissolved in water. Corrodes copper and steel (economizer shown).1 ppm O2 = 1 mg/L = 1000 ppb = 1000 µg/L

Dissolved Oxygen Effect on Copper CorrosionDissolved Oxygen Effect on Copper Corrosion

0

2

4

6

8

10

12

14

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0 50 100 150 200 250 300 350 400 450Temperature °F

Corro

sion

Rate

,mp y

70Cu/30Ni (Alloy 715) 3 ppb O2 100-200 ppb H70Cu/30Ni (Alloy 715) 200 ppb O2 25 ppb H90Cu/10Ni (Alloy 706) 3 ppb O2 100-200 ppb H90Cu/10Ni (Alloy 706) 200 ppb O2 25 ppb H

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Dissolved OxygenDissolved Oxygen

Normal ValuesMill Water or Demineralized Water

Saturated (8,000 - 14,000 ppb)Condensate: 10 - 100 ppb O2

Feedwater: <5 - 10 ppb O2

SourcesAir Leaks

Where Water Leaks Out, Air Leaks InMill Water In-leakage

0.1% Raw Water = 8 - 14 ppb O2

Dissolved Oxygen Control: DeaeratorDissolved Oxygen Control: Deaerator

SteamInlet

Trays

Distributor NozzlesVentWater Inlet

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Deaerator Spray Nozzles And TraysDeaerator Spray Nozzles And Trays

Oxygen Scavengers Oxygen Scavengers –– Carbohydrazide ExampleCarbohydrazide Example

Oxygen Scavenging (Reduces Oxygen) Oxygen + Carbohydrazide → Inerts + Carbonic Acid

PassivationRed Rust + Scavenger → Black Rust + Carbonic Acid

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Oxygen Scavenger FeedOxygen Scavenger Feed

UnderfeedCopper Corrosion in Steam/Condensate SystemPitting of Economizer

OverfeedFAC: Flow Accelerated Corrosion and Rupture of Steel Pipe Lines (e.g., Feedwater Line)Decomposition Products

QuestionsQuestions

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Hardness In Generation Bank TubeHardness In Generation Bank Tube

Hardness Scale In Generation Bank Tube, Dispersant TreatmentWithout Dispersants, Gray Mayonnaise Deposits Are In Drums

Hardness Hardness –– DefinitionDefinition

Mainly the Calcium (Ca) and Magnesium (Mg)Precipitates and Forms Hardness Scale In BoilerPrecipitation Can Result in Decreased Boiler pH

H2SO4+2Na2SO4+Ca3(PO4)2→2Na2HPO4+3CaSO4

Sulfuric Acid+Sodium

Sulfate+Calcium Phosphate→Sodium

Phosphate+Calcium Sulfate

Acid+Salt+Sludge→Phosphate+Hardness

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Hardness Hardness -- LimitsLimits

Expected Values (ppm CaCO3)Feedwater and Turbine Condensate: 0.0Process Condensate 0.0 – Trace

SourcesMill Water In Condensate/FeedwaterProblem In Makeup Demineralization System

Control of Hardness: Prevent IntrusionControl of Hardness: Prevent Intrusion

Condensate/Feedwater

CoolingWater Drain

Two Isolation ValvesFor HP Service

ThrottlingValve

Drain

Condensate/FeedwaterPump Discharge

Pump Seals

Seal Water

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Phosphate (POPhosphate (PO44))

Amount of Sodium Phosphate Dissolved in Boiler WaterUnits: ppm PO4 = mg/L PO4

Purpose: Stabilizes pHPrecipitates Hardness as Softer DepositsBackup Indication of Hardness Contamination

Phosphate/pH Control CurvesPhosphate/pH Control Curves

10.5

10.0

9.5

8.5

9.0

8.0 6 10 14 18 22 26 30

pH

Phosphate, mg/L

3.0

2.4

Na:P

OM o

larR

a tio4

Equilibrium Line (1 ppm NaOH)

1500 psig

(10.3 MPa)

1200 psig(8.3 MPa)

800 psig(5.5 MPa)

2.7

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Phosphate Effect on Boiler Water pHPhosphate Effect on Boiler Water pH

Sodium-To-PhosphateMolar Ratio

Blowdown

Phosphate, mg/L

pH

NaOH

TSP

DSP(MSP)

3.0

2.62.4

2.2

2.1

2.0

Summary: What Should You Know?Summary: What Should You Know?

Top Chemistry Parameters in Steam/Water CycleConductivity µS/cmpHDissolved Oxygen, ppb O2 (and Oxygen Scavengers)Hardness, ppm CaCO3

Phosphate, ppm PO4

Steam/Water Cycle, Basic ComponentsOther (See Appendices)

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AppendicesAppendices

A: Makeup Water TreatmentB: Condensate Collection and TreatmentC: Feedwater Treatment SystemD: Boiler Water TreatmentE: Steam Purity ConsiderationsF: Additional Chemistry TestingG: Preventive MaintenanceH: Personnel TrainingI: Chemical Cleaning

For More InformationFor More Information

TAPPI Technical Information PapersTIP 0416-03 – Water Quality and Monitoring Requirements for Paper Mill Boilers Operating on High Purity Water, 1999TIP 0416-04 – Design Engineer Decision Tree: Paper Mill Boiler Feedwater, 1999TIP 0416-05 – Response to Contamination of High Purity Boiler Feedwater, 2000TIP 0416-06 – Keys to Successful Chemical Cleaning of Boilers, 2000