WHY ?WHY ?Boiler water TreatmentBoiler water Treatment
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Vivek Pratap SinghVivek Pratap Singh Mechanical EngineerMechanical EngineerIndia Glycols LimitedIndia Glycols Limited
[email protected]@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