1

Boiler Water Boiler Water TreatmentTreatment

Training Handouts .

AGD

Boiler Water SystemBoiler Water Systempre-treatment Feed Tank

Feed pump Condensate

Continuous Blowdown

s s s

s

Boilers

s

s

s Sample pointPlant Process

Water

Column

Receiver

3

Benefits Of Using SteamBenefits Of Using Steam High Heat Content. Gives up heat at constant temperature. Produced from water which is cheap

and readily available. It is clean, odourless and tasteless. Can be used to generate power. Can be easily distributed and controlled.

4

Types 0f BoilersTypes 0f Boilers

Coil type Smoke tube Water tube Spreader stroker

5

Major ProblemsMajor Problems

Scaling corrosion Priming / Foaming Silica carryover Caustic embrittlement / cracking

Problems Caused By Impurities

7

Water Water Impurities

Dissolved Gases O2/CO2

Hardness

High TDS, SS, Alkalinity and Organic Matter

High OH- Alkalinity

Problems

Corrosion

Scaling Ca/Mg salts Carbonates Phosphates Silicates

Foaming/Priming

Caustic embrittlement/ Grooving

8

EFFECT OF SCALING, EFFECT OF SCALING, CORROSION, CARRY-OVER ON CORROSION, CARRY-OVER ON

BOILER SYSTEMBOILER SYSTEM Reduction in heat transfer Severe elevation of metal/tube temperature Promotes under deposit corrosion - pitting Loss of construction material Failure of boiler tubes Water losses Increased maintenance cost Unplanned shut downs Ultimately, increased operational costs and loss of

productivity.

PretreatmentInternal Boiler

Condensate return line treatment

Heat Treatment

10

1.0 System: Feed 1.0 System: Feed Problems Causes Treatment

Deposits Thermal decomposition andprecipitation of Alkalinehardness

Precipitation of non-alkalinehardness , by carbonate ,alkali or orthophosphateadded for deposit control

Elevation of temperature

DepositControllers

Corrosion Dissolved Oxygen

Low pH

Oxygen ScavengersNeutralising Amines

11

2.0 System : Boiler Drum2.0 System : Boiler Drum

Problems Causes Treatment

Deposits Precipitation ofHardness

Silica

Metal Oxides

Deposit Controller

Keep below the limitsrecommended for theparticular boiler pressures

Control pH>9.4

Disperants

Corrosion Oxygen and LowpH

Feed Treatment before Entering boiler

12

2.0 System: 2.0 System: BoilerDrumBoilerDrum

Problems Causes Treatment

Foaming High Dissolved andSuspended sollids

Contamination in feedwater eg. Oil, Organics ,Sugars etc.

Antifoams

Priming Mechanical faults, PoorOperation eg. Too high awater level, High loads,Sudden steam demand

No chemicaltreatment

13

3.0: System:Steam / 3.0: System:Steam / CondensateCondensate

Problems Causes Treatment

Deposits Carry over fromdrum

Silica Volatalisation

Antifoam

Limit SiO2 controlpH>9.4 in the drum water

Corrosion Oxygen ingress Volatile oxygen scavenger

Low pH Volatile neutralising amines inboiler

Boiler Water TreatmentBoiler Water TreatmentNo Scale: Heat transfer surfaces . free from Scale, sludge, . & depositsNo corrosion: Surfaces covered . by film of magnetitePure steam:Elimination of . carryoverSafe Operation: Prevention of . sludge in the water . level & blow down control .

Deposit FormationDeposit Formation

16

Deposit FormationDeposit Formation

Caused by hardness salts ppting,- Reduced solubility with increased temp.& increased conc. due to steam formation

Scale: occurs at the point of steam . generation sludge: occurs in bulk water & deposit on . metal surfaces

Lowers thermal conductivity Reduces boiler efficiency Increases fuel consumption

17

Deposits - Effects on MetalDeposits - Effects on Metal

Furnace temp. over 2500 deg F Metal deforms at 900 deg F Water temp 338 deg F (100 psig)

. 546 deg F (1000 psig) Deposits form insulating barrier, tolerence

depends on nature & heat tranfer of deposite

18

Thermal Conductivities Thermal Conductivities ( BTU .ft / ft2.hr.deg F )( BTU .ft / ft2.hr.deg F )

CaCO3 1.10 Ca3(PO4)2 2.20 CaSO4 0.90 Fe2O3 0.35 SiO2 (Quartz) 0.97 Carbon steel 30.0 Copper 218

19

Scale Deposition Scale Deposition PotentialPotential

Steam Production kg/hr

10,000 20,000 30,000 40,000

0.5

4

10 ppm hardness

5 ppm hardness

2ppm hardness

Tonnes

1.0

1.5

2.0

2.5

3.0

3.5

Tonnes/Year Entering Boiler

SCALE / DEPOSIT CONTROLSCALE / DEPOSIT CONTROL

21

Deposit ControlDeposit Control Correct Pre-Treatment of Feed Water Hardness Precipitation.

ppted as CO3-2 or PO4

-3 in presence of alkali.

Add sludge conditioners-polymers. Metal Oxides

Dispersed with phosphonate + polymer.

SilicaMainly present as Silicic acid H2SiO3

Decomposes above pH 9.4 into ionsTreatment

pH>9.4Keep below limits specified

22

pH and POpH and PO4 4 ConcentrationConcentration

Below curve

all alkalinity in the form of phosphate

Above curve

Free caustic present

PO4- conc in ppm10 3020 40 50 60 70

pH

9.2

9.4

9.6

9.8

10.8

10.0

10.6

10.2

10.4

80 90

CORROSION CONTROLCORROSION CONTROL

24

CorrosionCorrosion

Presence of Oxygen, causing ferric oxide rust ,Fe2O3

Fe +2H2O ---> Fe(OH)2 + H2 Under favourable conditions oxide reduces

to magnetite,Fe3O4,a very thin protective adherent film/layer 3Fe(OH)2 ---> Fe3O4 + 2H2O + H2

Magnetite film is most stable between pH 10.5 - 11.5

25

Corrosion ControlCorrosion Control

Removal of oxygen *Mechanical Deaeration *Scavenging by chemicals

Neutralising carbon dioxide

26

Mechanical DeaerationMechanical Deaeration Steam or Vacuum is used

Design to remove gases depends on: - Solubility of gases - Partial pressures - Operating temperatures

Technique employed : - To reduce partial pressure - Continuously extract evolved gases

Vacuum DeaeratorVacuum Deaerator

28

Oxygen Scavenger Oxygen Scavenger ReactionsReactions

Hydrazine N2H4 + O2----------> N2 + 2H2O Sulphite 2Na2SO3 + O2 ---------->2Na2SO4

Diethylhydroxylamine (DEHA) C2H5

NOH + [O] --> 2CH3COOH + 2N 2 + H2O

C 2H5

29

SulphiteSulphiteLimitations: Adds to boiler water TDS

Reaction slower at low temp

At max temp/press (5400F /950 psig) Na2SO 4 + H2O---> NaOH + H2SO3 H2SO3-------> H2O + SO2

It can undergo auto-oxidation/reduction 4Na2SO3------>3Na2SO4 + Na2S

Both SO2 and Na2S are corrosive

30

HydrazineHydrazine Any Excess Hydrazine breaks down to give Ammonia

3N2H4 ------> 4NH3 + N2

Small amounts < 0.5 ppm useful to neutralise CO2

Metal Passivator

6Fe2O3 + N2H4 -----> 4Fe3O4 + 2H2O + N2

Non-Volatile -----> Not available in return line

Carcinogenic

31

Di-Ethyl-Hydroxyl-Amine Di-Ethyl-Hydroxyl-Amine DEHADEHA

Non-Toxic

LD50 values---> 2190 mg/kg

(RATS, ORAL)

-------> 59 mg/kg for N2H4

Volatile : Available in return condensate line Does not impart any solids to Boiler Drum Water 1.24 ppm DEHA 1 ppm O2

Forms stronger magnetite film

Reaction Rates Of Oxygen Reaction Rates Of Oxygen Scavengers At 70Scavengers At 7000F And pH 8.5F And pH 8.5

10 20

2.0

4.0

6.0

8.0

10.0

DEHA

Catalysed Hydrazine

Hydrazine

Catalysed Sulphite

D.O. ppm

Catalysed DEHASulphite

Contact Time In Minutes

Reaction rates of oxygen Reaction rates of oxygen scavengers at 70scavengers at 7000F& pH 11F& pH 11

1.0 2.0 3.0

2.0

4.0

6.0

8.0

10.0

Catalysed Hydrazine

Catalysed DEHA

Catalysed Sulphite

Time Minutes

D.O.,ppm

Ammonia Generated By Ammonia Generated By DEHA and HydrazineDEHA and Hydrazine

100 200 300 400 500

0.2

0.4

0.6

0.8

1.0

DEHA

Hydrazine

Temperature (0F)

ppm NH3

Generated

per ppm

Product

Ability Of Catalysed Hydrazine to reduce ferric iron to ferrous

0.1 0.2 0.3 0.4 0.5 0.6

2.0

4.0-

6.0

8.0

10.0 Catalysed Hydrazine

Uncatalysed Hydrazine

Catalysed Sodium Sulphite

Hydrazine Concn in Feed Water (ppm)

Iron reduced

from ferric

to ferrous

36

TanninsTannins

Vegetable Tannins--Absorb O2 in alkaline Condition

Tannins form metal complexes & act as corrosion inhibitors

Decompose at high temp. Used in low press. boilers

useful at low temp. ,for protecting feedline

37

Carbon dioxide Carbon dioxide CorrosionCorrosion

Carbon dioxide is present both in free & combined form

CO2 + H2O <---> H2CO3 ( H2O.CO2 ) . - + H2CO3 <--->HCO3 + H (pK=4.2 ) . -2 + HCO3 <---> CO3 + H (pK=8.3)

Free CO2 is zero above pH 8.3 ,BFW is therefore neutralised to pH 8.5 ~ 9.0

38

Carbon Dioxide Carbon Dioxide CorrosionCorrosion

CO2 is released on heating in the drum _ _2 2HCO3 + Heat ----> CO3 + H2O +CO2 _2 _ CO3 + H2O + Heat ----> OH + CO2

Fe + 2H2CO3 ----> Fe[HCO3]2 + H2 Soluble Fe(HCO3)2 Can Precipitate as FeO, Fe3O4, FeCO3 in

presence of O2 in codensate line

39

Return Lines CorrosionReturn Lines Corrosion When steam condenses O2 & CO2 dissolve

and produce dil.carbonic acid containing O2

This codensate will corrode return system O2 causes pitting, while CO2 will channel out

as grooving Corrosion products will deposit in traps &

strainers, and may block narrow-bore returns

40

Return Line Corrosion Return Line Corrosion ProtectionProtection

Pretreatment - De-alkalisation / . De-mineralisation * . Deaeration

Oxygen Scavenging (Volatile) - D.E.H.A Use of Volatile Neutralising Amines to

keep BFW & condensate pH > 8.5 Filming Amines

*Softening Will not remove alkalinity & should be avoided

41

Volatile Oxygen Volatile Oxygen Scavenging (V.O.S)Scavenging (V.O.S)

DiEthylHydroxylAmine (D.E.H.A) Volatile hence passed into steam

(Distribution ratio 1.26). Removes Oxygen directly from the

condensate Reduces corrosion and also promotes

formation of an adherent magnetite film which gives additional corrosion protection.

42

Volatile Oxygen Volatile Oxygen Scavenger (V.O.A)Scavenger (V.O.A)

Some pH elevation may be attributed to DEHA

As a RLT DEHA should be dosed in combination with neutralising Amines.

43

Neutralising AminesNeutralising Amines

Steam volatile Alkaline materials which prevent corrosion caused by carbon dioxide

Amine reacts with carbonic acid to form Amine Carbonates or Bicarbonates and fix CO2. Elevation of pH to above 8.5 minimises the corrosion rate

44

Neutralising AminesNeutralising Amines Distribution ratio Concentration of Amine in vapour phase

Concentration of Amine in liquid phase.

High D.R= High volatility - Protects Cold End Low D.R. = Low Volatility - Protects Hot End

Single Neutralising Amines can be used but, more often blend of amines with differing Distribution Ratios is employed to maximise system protection. Neutralising Amines are also used in combination with V.O.S and with Filming Amines.

45

Neutralising Neutralising AminesAmines

Amine DistributionRatio

Protects

CycloHexylAmine 2.60 “COLD END”

D.E.A.E 1.45 General

Morpholine 0.48 “HOT END”

A.M.P. 0.30 “HOT END”

46

Filming AminesFilming Amines Filming amines contain a cationic amine group

& a long hydrocarbon chain (hydrophobic) Form an impervious, Non-Wettable film on

metal surfaces by attracting amine groups Steam condenses as a film & insulates heat

transfer surfaces. With filming amines the hydrophobic film

promotes condensation as droplets & increases heat transfer ( Very useful on a paper drying roller )

47

Primary AminesPrimary Amines

Primary Amines form films which completely cover metal surface giving excellent corrosion protection ( Octadecylamine - 0.5 ~ 2.0 ppm )

Insoluble - applied as an emulsion Incompatible with other products -

Separate Dosing system required.

48

Secondary AminesSecondary Amines

Secondary Amines form less efficient films. Should be used in conjunction with neutralising Amines (e.g. Blended products)

Compatible with other products - can use same Dosing system

49

Filming AminesFilming Amines

Filming Amines dosed to maintain Film Integrity

Over Dosing can cause Blockages Dosing must be carefully controlled

especially when applied to a previously corroded system

Should be introduced on a gradual basis.

50

Silica CarryoverSilica Carryover Silica is present as silicic acid, Si(OH)4 It dissociates in alkaline condition : .

_ _ Si(OH)4 + OH ---> H2SiO3 + H2O

Volatile silicic acid gets converted to soluble silicate ion above pH 9.5

As pressure increases ( B.P.Temp . Increases) Silica becomes more volatile,Silica content is therefore kept within limits as per boiler pressure

Silica in Boiler Water - Relationship with Pressure

Boiler water pH > 10.3

Boiler water pH<9.0

Silica , ppm

Maximum Silica Content in Boiler Water to keep silica < 0.02 ppm in steam

25002300210019001700150013000.0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

Press.,psig

52

Caustic Caustic Embrittlement Embrittlement

Under following conditions steel is subjected to intercrystalline cracking :

Boiler must be subject to high stress Boiler water must contain free NaOH

Rivetted flanges & rolled-in tube ends are more prone

53

Inhibition Of Inhibition Of CrackingCracking

For HP & MP boilers - use zero caustic / co-ordinated phosphate treatment (normally stress relieved tubes are used)

for LP boilers following chemicals may be used: *NaNO3 - keep NaNO3 / T.Alk as CaCO3 ratio above 0.4 *Na2SO4 - keep Na2SO4 / NaOH ratio above 2.5

54

PrimingPriming

Ejection of boiler water into the steam take-off

Reasons: *Too high drum water level *Operating boiler below design pressure *Operating at higher design capacity

Controlled by strictly adhering to operating conditions

55

FoamingFoaming Pure water does not foam & steam bubbles

are large & burst quickly Following causes foaming by altering

surface tension- reduce bubble size: *High suspended solids *High alkalinity *High dissolved solids *Contamination of oils &other surfactant

0.1 - 0.5 ppm antifom(certain organic compounds) cause bubbles to coalse

56

Recommended Water Characterstics For Water Recommended Water Characterstics For Water Tube BoilersTube Boilers

BS 2486 : 1978BS 2486 : 1978Pressure at boiler outlet(Bar)/PSIG

20300

40600

60900

801200

1001500

1201800

>130

Boiler Feed Water At Economiser inlet

TH mg/l as O2 maxPHOxygen Mg/l as O2 maxTotal solids , Alkalinity silicaOilOrganic MatterFe + Cu +Ni Mg/l as Max.

108.5-9.50.05* *ND-

28.5-9.50.02* *ND-

Boiler

0.58.5-9.50.01* *ND-0.02

Water

ND8.5-9.50.01* *ND-0.02

ND8.5-9.50.005* *ND-0.01

ND8.5-9.50.005* *ND-0.01

ND8.5-9.50.005* *ND-0.01

Na phosphate mg/l as Na2PO4

OH Alk. Mg/l as CaCO3 , Min.Total Alk. Mg/l as CaCO3 , MaxSilica , mg/l as SiO2 , Max

Na Sulphite mg/l as Na2SO3

OrHydrazine mg/l as N2H4

Susp solids mg/l MaxTDS mg/l max.Chloride mg/l as Cl- . Max

50-100300700 < 0.4 of

30-50

0.1-1.02003000-

30-70150500Caustic Alkalinity20-40

0.1-0.5502000-

29-506030020

15-30

0.05-0.3-1200-

10-403020010

10-20

0.05-0.1-700-

5-2010100!

-

!-35010

3-10540!

-

!-1005

!210!

-

!-15!

57

Shell Boiler Operating ParametersShell Boiler Operating ParametersType of boiler

Boiler prBar PSIG

LancashireCornish

150

Verticak Fire Tube

150

Economic/Vertical Wt.

150

Modern Packaged

350

Feed water----------------pH ---- ------- ------ 8.5-9.5

Tot Hardness Max, 200 100 40 2

Fe,Ni,Co,Max --- ---- ---- 0.2

Oxygen

Oil

Boiler water------------------Caustic alk. Min.

Tot. alk. Max.

Phosphate asPO4

Sulphite Na2SO4

OrHydrazine N2H4

Suspended solids max

TDS max

-----

Nil

200

------------------------------------

------------------------------------

50-100

---

2000

8000

-----

Nil

250

-----------------------25%

------------30 - 60------

50-100

------

1000

5000

------

Nil

250

of TDS-----------------------

-------------------------------------

50-100

0.1-1.0

1000

5000/3500

-------

Nil

350

-----------------

-------------------

30-70

0.1-1.0

100

3500

All reserves are as ppm. Hardness and alkalinity reserves are expressesd as CaCO3. The operating caustic alkalinity is assumed to be half the maximum total alkalinity

58

Boiler Water Boiler Water Treatment Treatment

Programming Programming CalculationsCalculations

59

Survey DataSurvey Data Raw water analysis Pretreatment Feed water analysis Feed water Temperature Steam output and input pressure water consumption Condensate Return Steam Applications

60

Calculation stepsCalculation steps !. Determine Feed water quality 2. Determine oxygen scavenger dose 3 . calculate the maximum permissible boiler conc. 4. calculate Alkalinity demand 5. calculate phosphate requirement 6. calculate sludge conditioner dosage 7. calculate return line treatment requirement 8. Determine blow down rate 9. convert product dosage ppm to weight 10. calculate cost of programme

61

Determine Feed Water Determine Feed Water qualityquality

Condensate Return% = 1 - Feed water Cl . Makeup Cl

% Raw water usage = 100- Condensate . Return %

Feed water Quality= Make-up Quality x . % Make-up water used

(Assuming No Contamination of condensate has occurred)

{ } x 100

62

Determine Oxygen Determine Oxygen Scavenger DoseScavenger Dose

Sulphite Requirement

[ Feed water O2(ppm) X 8 ] +Sulphite Reserve/C

Hydrazine Requirement [Feed water O2(ppm) X 1 ]

+Hydrazine Reserve/C

63

Feedwater Temp Feedwater Temp Dissolved oxygenDissolved oxygen

100 212 95 203 90 194 85 185 80 176 75 167 70 158 65 149 60 140 55 131 50 122 45 113 40 104 35 95 30 86 25 77 20 68

0 0.8 1.6 2.2 2.9 3.4 3.9 4.3 4.7 5.2 5.6 6.1 6.6 7.1 7.5 8.1 8.8

0C Temp. 0F D.O.ppm

64

Determine Maximum Permissible Determine Maximum Permissible Boiler ConcentrationsBoiler Concentrations

C Max TDS = ________TDS MAX LIMIT_________

TDS FEED + SULPHITE DOSED

C Max ALKALINITY = ALKALINITY MAXIMUM TOTAL ALK. FEED - A

A is the Bisulphite allowance . Some Indion products are Bisulphite based, check product application guidelines for allowance.

C Max SILICA = MAX ALLOWABLE BOILER SILICA ACTUAL SILICA IN FEED

.

65

Alkalinity DemandAlkalinity Demand

Alkalinity Demand = {(FWAlk - FW TH - Bisulphite Allowance) x Cmax}-

Alk Res

Alkalinity reserve is normally taken as 850 ppm for low pressure boilers

If demand is negative then no extra alkali is required

Dose 0.8 ppm Sodium Hydroxide per 1 ppm of Alkalinity demand

66

Determination of Determination of Phosphate RequirementPhosphate Requirement

Assuming a product is 100% phosphate as PO4 then dosage is given by

0.63 ppm product per 1 ppm CaH + 30/C max

67

Checking Sludge Checking Sludge conditioner dosageconditioner dosage

Boiler Sludge Conditioner Dose =

Sludge Conditioner Conc ( 200ppm) COC X Product Factor

Typical Sludge conditioner levels are minimum 200 ppm for normal operations and minimum 300 ppm for on-line cleans

68

Calculate Return Line Calculate Return Line treatment requirementtreatment requirement

Dose of RLT Products is based on maintaining condensate pH 8.5

This in turn depends on CO2 generated in the boiler drum.

69

Determination Of Determination Of BlowdownBlowdown

%Blowdown = 100 X S . T-S Calculated as %of Evaporation rate

% Blowdown = 100 . . C max Calculated as % of Feed water

Feedwater rate.

S - Feedwater TDS

T - Boiler water Maximum TDS

70

Conversion of dose rates to kg Conversion of dose rates to kg product per dayproduct per day

Say, Water Usage (Evaporation + Blow Down) = F Tons/Day

Say, product dose = X ppm

Then, Product Required (Kg/Day) = F x X1000

71

Water Water Losses Losses

72

Water Losses From Steam Water Losses From Steam SystemSystem

Evaporation Of steam Loss of Condensate steam Boiler leaks Blowdown

73

Uncontrolled water Uncontrolled water LossesLosses

Steam boilersWaste waterWaste fuelWaste chemicalLead to poor control of inhibitor reserves

Lead to over running of pretreatment plant, Fuel, increased chemical consumption