WHY ?WHY ?Boiler water TreatmentBoiler water Treatment

BBYY

Vivek Pratap SinghVivek Pratap Singh Mechanical EngineerMechanical EngineerIndia Glycols LimitedIndia Glycols Limited

vivekpsingh.mech@rediffmail.comvivekpsingh.mech@rediffmail.com

Types Of BoilersTypes Of Boilers

Coil Type

Fire Tube

Water Tube

Coil Type

Fire Tube

Water Tube

ASME Guidelines for Water Quality in Modern Industrial Water Tube BoilersASME Guidelines for Water Quality in Modern Industrial Water Tube Boilers

Drum Iron Copper Total Silica Total Specific

Pressure (ppm Fe) (ppm Cu) Hardness (ppm SiO2) Alkalinity**Conductan

ce

(psi)(ppm

CaCO3)(ppm

CaCO3)(micromho

s/cm)(unneutrali

zed)

0-300 0.1 0.05 0.3 150 700* 7000

301-450 0.05 0.025 0.3 90 600* 6000

451-600 0.03 0.02 0.2 40 500* 5000

601-750 0.025 0.02 0.2 30 400* 4000

751-900 0.02 0.015 0.1 20 300* 3000

901-1000 0.02 0.015 0.05 8 200* 2000

1001-1500 0.01 0.01 0 2 0*** 150

Boiler Feed Water Boiler Water

Types of Pretreatment EquipmentTypes of Pretreatment Equipment

•Primary• Clarifiers• Lime Soda Softener• Sodium Zeolite Softener

Secondary• Demineralizer• Dealkalizers• Reverse Osmosis

•Primary• Clarifiers• Lime Soda Softener• Sodium Zeolite Softener

Secondary• Demineralizer• Dealkalizers• Reverse Osmosis

Problems associated with boiler water Problems associated with boiler water

• Scaling

• Corrosion

• Priming (formation of droplets)• Carryover in the steam (of volatile

minerals)

• Scaling

• Corrosion

• Priming (formation of droplets)• Carryover in the steam (of volatile

minerals)

ScaleScale

Accumulation of material on boiler surfaces that can cause overheating as well as circulation restrictions.

Both conditions frequently result in unscheduled Shutdowns.

Accumulation of material on boiler surfaces that can cause overheating as well as circulation restrictions.

Both conditions frequently result in unscheduled Shutdowns.

ScaleScale

ScalingScaling

Scale formation is a function of two criteria:

1. The concentration and solubility limits of the dissolved salt

2. The inverse solubility (proportional to temperature) property of some salts

Scale formation is a function of two criteria:

1. The concentration and solubility limits of the dissolved salt

2. The inverse solubility (proportional to temperature) property of some salts

ScaleScale

 Many solids, soluble in boiler feedwater, precipitate in the boiler water. This happens due to change in chemistry of water when going from feedwater to boiler water conditions, inverse solubility of some salts like carbonate which will combine with calcium

to form calcium carbonate, a relatively insoluble salt. Magnesium hydroxide and iron oxide are also produced by changes in water chemistry.

 Many solids, soluble in boiler feedwater, precipitate in the boiler water. This happens due to change in chemistry of water when going from feedwater to boiler water conditions, inverse solubility of some salts like carbonate which will combine with calcium

to form calcium carbonate, a relatively insoluble salt. Magnesium hydroxide and iron oxide are also produced by changes in water chemistry.

Effect of ScaleEffect of Scale

Scale Formation ReactionsScale Formation Reactions

Ca(HCO3)2       = CaCO3  +  CO2  +  H2O

Fe++  +    2HCO3- = Fe(OH)2  + 2CO2

Mg(HCO3)2      = Mg(OH)2  +  2CO2

Ca(HCO3)2       = CaCO3  +  CO2  +  H2O

Fe++  +    2HCO3- = Fe(OH)2  + 2CO2

Mg(HCO3)2      = Mg(OH)2  +  2CO2

How Bad Are Iron Deposits?How Bad Are Iron Deposits?

00

11

22

33

44

55

66

77

1/641/64

Iron + Silica

High Iron Content

"Normal" Scale

1/321/32 3/643/64 1/161/16

Scale Thickness - InchesScale Thickness - Inches

En

erg

y L

oss

%E

ner

gy

Lo

ss %

Prevention of scalingPrevention of scaling

Solubilizing programs

Precipitating Programs

Coordinated phosphate - pH programs.

Congruent phosphate

Filming amines

Solubilizing programs

Precipitating Programs

Coordinated phosphate - pH programs.

Congruent phosphate

Filming amines

How Does Corrosion Occur in a Boiler?How Does Corrosion Occur in a Boiler?

How Does Corrosion Occur in a Boiler?How Does Corrosion Occur in a Boiler?

From Oxygen in the FeedwaterFrom Oxygen in the Feedwater

Oxygen CorrosionOxygen Corrosion

How Does Corrosion Occur in a Boiler?How Does Corrosion Occur in a Boiler?

From Oxygen in the Feedwater

From Acid Conditions in the Boiler

From Oxygen in the Feedwater

From Acid Conditions in the Boiler

How Does Corrosion Occur in a Boiler?How Does Corrosion Occur in a Boiler?

From Oxygen in the Feedwater

From Acid Conditions in the Boiler

Caustic Attack

During an Idle Period

From Oxygen in the Feedwater

From Acid Conditions in the Boiler

Caustic Attack

During an Idle Period

Corrosion in Boiler - OxygenCorrosion in Boiler - Oxygen

Dissolved oxygen in the feedwater can attack the feedwater line, heaters, and the economizer. Oxygen induced corrosion is an electrochemical reaction and often results in localized pitting of the metal surface.The rate of reaction and severity of this type of corrosion will depend upon the level of dissolved oxygen, temperature, and pH of the feedwater.Corrosion of steel is a spontaneous electrochemical reaction that occurs between iron and oxygen. The overall reaction is: Fe + ½ O2 + H2O

Fe(OH)2

Contd……Contd……

Oxygen attack on steel can be decreased by maintaining an alkaline pH and limiting the oxygen concentration.The factors affecting oxygen scavenging reaction rates include:• Oxygen concentration • Presence of a catalyst • Reaction time • pH • Temperature • Scavenger feed rate and decomposition

Oxygen attack on steel can be decreased by maintaining an alkaline pH and limiting the oxygen concentration.The factors affecting oxygen scavenging reaction rates include:• Oxygen concentration • Presence of a catalyst • Reaction time • pH • Temperature • Scavenger feed rate and decomposition

Acidic Boiler WaterAcidic Boiler Water

CAUSTIC GOUGING

BOILER WATER ENTERS THROUGH POROUS DEPOSITS

ESCAPES AS STEAM THROUGH CHIMNEYS FORMEDIN POROUS DEPOSITS

A LOCALISED BOILER FORMS LEADING TO CONCENTRATIONOF SOLIDS WITH NO PROVISION OF BLOWDOWN Steam Boiler Water

Conc NaOH

AS A RESULT CAUSTIC CONCENTRATES UPTO ABOUT 1%(10,000 ppm) AND ABOVE,AND CONC KEEPS INCREASING

Prevention of CorrosionPrevention of Corrosion

Means of Removal of Dissolved gasses Means of Removal of Dissolved gasses

Mechanically

Chemical

Mechanically

Chemical

MechanicalMechanical

Degasser

Deaerater

Tray type

Spray type

Degasser

Deaerater

Tray type

Spray type

Purpose of a DeaeratorPurpose of a Deaerator

• Remove Oxygen and Other Dissolved Gases from Feedwater

• Remove Oxygen and Other Dissolved Gases from Feedwater

Why is Deaeration Necessary?Why is Deaeration Necessary?

Why is Deaeration Necessary?Why is Deaeration Necessary?

• Oxygen Corrosive Mild Steel• Oxygen Corrosive Mild Steel

Why is Deaeration NecessaryWhy is Deaeration Necessary

• Oxygen Corrosive to Mild Steel

• Cheaper to Remove Most of the Oxygen with Steam than to Remove Chemically

• Oxygen Corrosive to Mild Steel

• Cheaper to Remove Most of the Oxygen with Steam than to Remove Chemically

Consequences of poor deaerationConsequences of poor deaeration

Oxygen PittingOxygen Pitting

ChemicalChemical

Sodium BiSulphite

Na2SO3

Hydrazine

DEHA

Carbohydrazide

Sodium BiSulphite

Na2SO3

Hydrazine

DEHA

Carbohydrazide

Condensate SystemCondensate System

Make-up Water

PrimaryPretreatment

SecondaryPretreatment

Steam Header

BoilerBoiler

Feedwater

Blowdown

ChemicalFeed

Systems

DeaeratorDeaerator

Condensate

Why you need a condensate recovery ?Why you need a condensate recovery ?

CorrosionCorrosion

How Does Corrosion Occur?How Does Corrosion Occur?

How Does Corrosion Occur?How Does Corrosion Occur?

Oxygen

Carbon Dioxide

Oxygen

Carbon Dioxide

Oxygen CorrosionOxygen Corrosion

Oxygen Enters the Steam/Condensate SystemOxygen Enters the Steam/Condensate System

Oxygen Enters the Steam/Condensate SystemOxygen Enters the Steam/Condensate System

From FeedwaterFrom Feedwater

Oxygen Enters the Steam/Condensate SystemOxygen Enters the Steam/Condensate System

From Feedwater

Draw in Under Vacuum as Steam Condenses

From Feedwater

Draw in Under Vacuum as Steam Condenses

Carbonic Acid CorrosionCarbonic Acid Corrosion

Carbon Dioxide Can Enter the Steam/Condensate SystemCarbon Dioxide Can Enter the Steam/Condensate System

From Breakdown of Feedwater AlkalinityFrom Breakdown of Feedwater Alkalinity

Carbon Dioxide Can Enter the Steam/Condensate SystemCarbon Dioxide Can Enter the Steam/Condensate System

From Breakdown of Feedwater Alkalinity

Drawn in Under Vacuum as Steam Condenses

From Breakdown of Feedwater Alkalinity

Drawn in Under Vacuum as Steam Condenses

Oxygen and Carbonic Acid CorrosionOxygen and Carbonic Acid Corrosion

How Can You Tell If You Have a Corrosion Problem?How Can You Tell If You Have a Corrosion Problem?

How Can You Tell If You Have a Corrosion Problem?How Can You Tell If You Have a Corrosion Problem?

If You Need to Replace LinesIf You Need to Replace Lines

How Can You Tell If You Have a Corrosion Problem?How Can You Tell If You Have a Corrosion Problem?

If You Need to Replace Lines

Testing for Iron in the Returned

Condensate

If You Need to Replace Lines

Testing for Iron in the Returned

Condensate

What Happens When You Cannot Stop Corrosion or Treat Your Condensate SystemWhat Happens When You Cannot Stop Corrosion or Treat Your Condensate System

What Happens When You Cannot Stop Corrosion or Treat Your Condensate SystemWhat Happens When You Cannot Stop Corrosion or Treat Your Condensate System

Dissolved Iron Turns to Iron ParticlesDissolved Iron Turns to Iron Particles

What Happens When You Cannot Stop Corrosion or Treat Your Condensate SystemWhat Happens When You Cannot Stop Corrosion or Treat Your Condensate System

Dissolved Iron Turns to Iron Particles

Particulate Iron Goes Into the Boiler

Dissolved Iron Turns to Iron Particles

Particulate Iron Goes Into the Boiler

What Happens When You Cannot Stop Corrosion or Treat Your Condensate SystemWhat Happens When You Cannot Stop Corrosion or Treat Your Condensate System

Dissolved Iron Turns to Iron Particles

Particulate Iron Goes Into the Boiler

Iron Deposits Are Formed

Dissolved Iron Turns to Iron Particles

Particulate Iron Goes Into the Boiler

Iron Deposits Are Formed