BOILER WATER TREATMENT THE POLYAMINE SOLUTION

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BOILER WATER TREATMENTTHE POLYAMINE SOLUTION
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Water cycle in the boiler house
RAW WATER
SOFTENER
Superheater
uses
Water meter
Deaerator
FFEED TANK
condenser
BOILER
BLOWDOWN
Dosing tank
CONDENSATE RETURN
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MAIN PROBLEMS

• Scaling
• Corrosion
• Carry over

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Raw water composition
Including
Sand, mud, colloidal organic material, and so on,
Suspended solids
Organic material in solution
Organic acid, vegetation rejection,
Cations
Anions
Dissolved salts
Calcium Ca2 Magnesium Mg2 Sodium
Na Potassium K etc...
Bicarbonates HCO3- Chlorides Cl- Sulfates
SO42- Nitrates NO3- etc...
Dissolved gas
Oxygen, carbonic gas, nitrogen
Micro-organisms
Algae, bacteria, fungi
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Usual water analysis
unit Observations
pH - Acidity or basicity
Total Hardness ppm CalciumMagnesium
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 mS/cm Water quality
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Feed water requirements
For Plt20 bar According prEN 12953-10 and 12952-12 standards
pH gt 8.5 gt 9.2
TH ppm CaCO3 lt 3 lt 2
Oxygen mg/L lt 0,1 lt 0.05
Oil and grease No lt 1 mg/L
Organic matters No TOC lt 1 mg/L lt 0,2 if Pgt40b
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Boiler water requirements
For Plt20 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 lt 1200 -
SiO2 in mg/L lt 200 lt 160
Conductivity µS/cm - lt 8000
PO4 in mg/L 30 à 100 lt 30
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Scale-forming salts
mg/L
CaSO
,2H
O
4
2
2200
(gypsum)
CaSO
4
(anhydrite
)
CaSO
,1/2H
O
4
2
(semi-hydrate)
300
CaCO
3
100
40 60 180
C
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SILICA
SiO2 in steam in ppm
SiO2 in boiler (mg/L)
Pressure in bar
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Basic corrosion process
Anodic reaction
H
O
2
Fe
-
2
OH
Fe
2
-
OH
-
2 e
-
OH
Fe(OH)
2


H

Cathodic reaction
2H
H
-

2 e
2
2 e
With dissolved oxygen
-
-

4 e

O

2 H
O


4 OH
2
2
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Local oxygen corrosion
Oxygen cannot reach the metal under the deposit,
which creates an anodic area.
O
2
O
2
O
2
-
OH

Fe
-
OH
-
e
-
e
-
e
The cathodic reaction is taking place where
oxygen can reach the metal.
Metal
Iron
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High temperature corrosion
3 Fe 4 H2O ? Fe3O4 4 H2
Shikorr reaction This reaction is catalysed by
dissolved oxygen.
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CO2 production by softened water

• 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

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Bicarbonate decomposition
decomposition
100
100 C
90 C
50
time mn
30 60 90 120
REACTION 1 2NaHCO3 ? Na2CO3 CO2 H2O
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Carbonate decomposition
Hydrolysis
100
50
10 20 30 40 50 P in bars
REACTION 2 Na2CO3 H2O ? 2 NaOH CO2
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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

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TRADITIONAL TREATMENT

• Phosphates
• Oxygen scavengers
• Dispersants, anti-scaling agents
• Neutralizing amines

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Oxygen scavengers

• MAIN OXYGEN SCAVENGERS
• sulfites
• Na2SO3 ½ O2 Na2SO4
• hydrazine
• N2H4 O2 N2H2O
• tanins

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MAIN DISADVANTAGES

• Toxicity hydrazine, morpholine
• Corrosion of copper and copper alloys
• Extra salinity added phosphates, sulfites
• Problems due to feedwater injection in steam

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POLYAMINE ALTERNATIVE 

• A combination of 2 main actions
• pH control
• Filming protection

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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

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VARIOUS ACTIONS

• ANTI-SCALING EFFECT
• ADSORPTION FILMING EFFECT
• PSEUDO-COMPLEX FORMATION WITH METALS
• DROP CONDENSATION

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ADSORPTION
3
3
1. Adsorption
2
2
2. Ion - ion
1
1
1
3. Hydrophobic bond
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PSEUDO-COMPLEXFORMATION
CH3
CH3
CH2
CH2
CH2
CH2
H
H
N
N
O
O
H
H
Fe
Fe
H
H
O
O
O
O
H
H
Fe
Fe
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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.
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INVESTIGATION OF THE FILM EXPERIMENTAL PROCEDURE
Potentiostat
I
mA
E
mV
Auxiliary electrode (Pt)
Reference electrode
Rotating disc electrode (steel)
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IMPEDANCE DIAGRAM
- jG (?.cm2)
HF loop film evidence
R (?.cm2)
Re
Rp
Cd
CHF
Cd
Re
Re
RHF
Rp
Rp
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Protection of boilertubes

• 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.

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Magnetite production experimental procedure
Emulsion water/steam 24
Incondensable gases
H2
Expansion condensation cooling
Boiler tube ? 23 w/cm2 P 100 bars TC
315 C
Make - up demineralized water
3 Fe 4 H2O ? Fe3O4 H2
Shikorr reaction
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Stability of the magnetite layer
H2 as vpm (volume per million)
Magnetite production
POLYAMINE injection
10
2 vpm during 72 hours
2
time
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HEAT EXCHANGE

• The polyamine film formed on metal surfaces does
  not affect the thermal exchange.
• Presence of polyamines increases the yield of
  condensers.

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THERMAL EXCHANGE
? in w/cm.C
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DROP CONDENSATION
Dh ()
5 4 3 2 1
Film condensation
ppm ODA
Drop condensation
0 1 2 3
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Toxicity vs inocuity

• Toxicity of hydrazine
• LD 50 60 mg / kg of weight
• Carcinogenic
• Inocuity of the polyamine
• LD 50 gt 2000 mg / kg
• Non carcinogenic

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CONCLUSIONS

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