BOILER WATER

TREATMENT

THE POLYAMINE SOLUTION

SOFTENER

BOILER

condenser

Dosingtank

Water meteruses

CONDENSATE RETURN

FFEEDTANK

BLOWDOWN

RAW WATER

Deaerator

Superheater

Water cycle in the boiler house

Scaling

Corrosion

Carry over

MAIN PROBLEMS

Including

Suspended solids

Organic material in solution

Dissolved salts

Dissolved gas

Micro-organisms

Sand, mud, colloidal organic material, and so on,

Organic acid, vegetation rejection,…

Cations : Anions :Calcium Ca2+

Magnesium Mg2+

Sodium Na+

Potassium K+

etc...

Bicarbonates

HCO3-

Chlorides Cl-

Sulfates SO42-

Nitrates NO3-

etc...Oxygen, carbonic gas, nitrogen

Algae, bacteria, fungi

Raw water composition

unit Observations

pH - Acidity or basicity

Total Hardness

ppm Calcium+Magnesium

p Alkalinity ppm OH and CO3

m Alkalinity ppm OH, CO3 and HCO3

Chlorides mg/L Determination Rc

T.D.S. mg/L Total dissolved salts

Conductivity S/cm Water quality

Usual water analysis

For P<20 bar

According prEN 12953-10 and 12952-12

standards

pH > 8.5 > 9.2

TH ppm CaCO3

< 3 < 2

Oxygen mg/L < 0,1 < 0.05

Oil and grease No < 1 mg/L

Organic matters

No TOC < 1 mg/L< 0,2 if P>40b

Feed water requirements

For P<20 bar

General, from

manufacturer

According prEN 12953-10 and

12952-12 standards

pH 10.5 to 11.5 10.5 to 12

p-Alk ppm CaCO3

- 50 to 750

m-Alk ppm CaCO3

< 1200 -

SiO2 in mg/L < 200 < 160

Conductivity µS/cm

- < 8000

PO4 in mg/L 30 à 100 < 30

Boiler water requirements

mg/L

CaSO4,2H2O(gypsum)2200

CaSO4,1/2H2O(semi-hydrate)

CaSO4

(anhydrite)

CaCO3300

100

40 60 180 °C

Scale-forming salts

SiO2 in steam in ppm

Pressure in bar

SiO2 in boiler (mg/L)

SILICA

Fe2+ + 2OH-

Fe

+ 2 e-

Fe(OH)2

H2O

OH-

+

H+

2H+H2

2 e +

With dissolved oxygen :4 e- + O2 + 2 H2O 4 OH-

OH-

2 e -

Basic corrosion process

Anodic reaction

Cathodic reaction

Fe ++

O2

O2

O2

Metal : Iron

Oxygen cannot reach the metal under the deposit, which creates an anodic area.

The cathodic reaction is taking place where oxygen can reach the metal.

e-e-

e-

OH-

OH-

Local oxygen corrosion

3 Fe + 4 H2O Fe3O4 + 4 H2

Shikorr reaction :

This reaction is catalysed by dissolved oxygen.

High temperature corrosion

BICARBONATES ARE DECOMPOSED IN CARBONATES BY HEAT WITH PRODUCTION OF CO2

CARBONATES ARE HYDROLYSED INTO CAUSTIC SODA WITH PRODUCTION OF CO2

THE REACTIONS : 2NaHCO3 Na2CO3 + CO2 + H2O

Na2CO3 + H2O 2 NaOH + CO2

CO2 production by softened water

REACTION 1REACTION 1 : :

2NaHCO2NaHCO33 NaNa22COCO33 + CO + CO22 + + H2OH2O

% decomposition

time mn

100

50

100 °C

90 °C

30 60 90 120

Bicarbonate decomposition

REACTION 2 :REACTION 2 :

NaNa22COCO33 + H + H22OO 2 NaOH + 2 NaOH +

COCO22

% Hydrolysis

100

50

10 20 30 40 50 P in bars

Carbonate decomposition

PURPOSE OF BOILER WATER TREATMENT

pH control of feedwater and boiler water Avoid precipitation of scaling salts: calcium

carbonate, silica, iron, copper Internal protection of boiler tubes and

drums Protection of condensate return lines

TRADITIONAL TREATMENT

Phosphates

Oxygen scavengers

Dispersants, anti-scaling agents

Neutralizing amines

MAIN OXYGEN SCAVENGERS

sulfites : Na2SO3 + ½ O2 Na2SO4

hydrazine : N2H4 + O2 N2+H2O

tanins

Oxygen scavengers

MAIN DISADVANTAGES

Toxicity: hydrazine, morpholine

Corrosion of copper and copper alloys

Extra salinity added: phosphates, sulfites

Problems due to feedwater injection in steam

POLYAMINE ALTERNATIVE  

A combination of 2 main actions

pH control

Filming protection

FILMING POLYAMINES

R-NH- CH2 3-n-NH2

n = 0 to 7

example : octadecylamine n = 0 R = straight carbon chain

with C12 minimum

and C18 predominant

VARIOUS ACTIONS

ANTI-SCALING EFFECT

ADSORPTION : FILMING EFFECT

PSEUDO-COMPLEX FORMATION WITH METALS

DROP CONDENSATION

ADSORPTION

1. Adsorption

2. Ion - ion

3. Hydrophobic bond

1 1 1

2 2

3 3

PSEUDO-COMPLEXFORMATION

Fe

CH3

CH2

N

CH2

O

HFe

H

O

H

O

H

H

H

Fe

CH3

CH2

N

CH2

O

FeO

H

OH

THE POLYAMINE FILM

Polyamines form a protective film on the metal surface.

This film has been evidenced by means of electrochemical measurements of corrosion and particulary by electrochemical impedance diagrams.

INVESTIGATION OF THE FILM

EXPERIMENTAL PROCEDURE

mAmV

IE

Auxiliaryelectrode

(Pt)

Referenceelectrode

Rotating discelectrode (steel)

Potentiostat

Re

Rp

Cd CHF

RHF

Re

Rp

Cd

- jG (.cm2)

R (.cm2)Re Rp

HF loop :film evidence

IMPEDANCE DIAGRAMIMPEDANCE DIAGRAM

Protection of boilerProtection of boilertubestubes

Polyamines stabilize the magnetite layer formation on the tubes of steam generators.

The study of the effect of POLYAMINE products on the Shikorr reaction (magnetite production) proves the efficiency of polyamines against corrosion.

Boilertube :

= 23 w/cm2

P = 100 barsT°C = 315 °C

Expansioncondensationcooling

Incondensable gases

Emulsion water/steam 24 %

Make - up :demineralized

water

3 Fe + 4 H2O Fe3O4 + H2

H2

Shikorr reaction

Magnetite production :experimental procedure

Stability of the magnetite layer

H2 as vpm (volume per million)

time

10

2

Magnetite production

POLYAMINE injection

2 vpm during 72 hours

HEAT EXCHANGE

The polyamine film formed on metal surfaces does not affect the thermal exchange.

Presence of polyamines increases the yield of condensers.

V D.I. water C = 100 ppm C = 1000 ppm0.5 m/s 0.17 0.167 0.1671.0 m/s 0.166 0.166 0.1661.5 m/s 0.165 0.165 0.165

in w/cm.°C

THERMAL EXCHANGETHERMAL EXCHANGE

Film condensation

Drop condensation

ppm ODA

(%)

5

4

3

2

1

0 1 2 3

DROP CONDENSATION

Toxicity vs inocuity

Toxicity of hydrazine: LD 50 = 60 mg / kg of weight Carcinogenic

Inocuity of the polyamine: LD 50 > 2000 mg / kg Non carcinogenic

CONCLUSIONS

Efficiency Simplicity Hydrazine free Non toxic Reduction of blowdown Improvement of condenser yield Cost-effective