Transcript BOILER WATER TREATMENT THE POLYAMINE SOLUTION

BOILER WATER
TREATMENT
THE POLYAMINE SOLUTION
Water cycle in the boiler house
RAW WATER
SOFTENER
Superheater
uses
Water meter
Deaerator
FFEED
TANK
condenser
BOILER
Dosing
tank
BLOWDOWN
CONDENSATE RETURN
MAIN PROBLEMS
 Scaling
 Corrosion
 Carry
over
Raw water composition
Including
Suspended solids
Organic
material in
solution
Dissolved salts
Sand, mud, colloidal organic material,
and so on,
Organic acid, vegetation rejection,…
Cations :
Calcium
Ca2+
Magnesium Mg2+
Sodium
Na+
Anions :
Bicarbonates HCO3Chlorides
ClSulfates
Dissolved gas
Potassium K+
Nitrates
etc...
etc...
Oxygen, carbonic gas, nitrogen
Micro-organisms
Algae, bacteria, fungi
SO42NO3-
Usual water analysis
pH
Total Hardness
p Alkalinity
m Alkalinity
Chlorides
T.D.S.
Conductivity
unit
ppm
ppm
ppm
mg/L
mg/L
mS/cm
Observations
Acidity or basicity
Calcium+Magnesium
OH and CO3
OH, CO3 and HCO3
Determination Rc
Total dissolved salts
Water quality
Feed water requirements
For P<20
bar
According prEN 1295310 and 12952-12
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
standards
Boiler water requirements
pH
For P<20 bar
General, from
manufacturer
10.5 to 11.5
10.5 to 12
p-Alk ppm CaCO3
m-Alk ppm CaCO3
SiO2 in mg/L
Conductivity µS/cm
PO4 in mg/L
< 1200
< 200
30 à 100
50 to 750
< 160
< 8000
< 30
According prEN
12953-10 and
12952-12
standards
Scale-forming salts
mg/L
CaSO4,2H2O
(gypsum)
2200
CaSO4
(anhydrite)
300
CaSO4,1/2H2O
(semi-hydrate)
CaCO3
100
40
60
180
°C
SILICA
SiO2 in steam in ppm
SiO2 in boiler (mg/L)
Pressure in bar
Basic corrosion process
Anodic reaction
H2O
Fe
Fe2+ + 2 OH
OH-
+ 2 e-
OH-
Fe(OH)2
+
H+
Cathodic reaction
2e
2e
-
+
+ 2H
H2
With dissolved oxygen :
4 e- + O2 + 2 H2O  4 OH-
Local oxygen corrosion
O2
OH-
O2
O2
Fe++
OH -
e-
e-
eMetal : 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.
High temperature corrosion
3 Fe + 4 H2O  Fe3O4 + 4 H2
Shikorr reaction :
This reaction is catalysed by dissolved oxygen.
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
Bicarbonate decomposition
% decomposition
100
100 °C
90 °C
50
30
60
90
REACTION 1 :
120
time mn
2NaHCO3  Na2CO3 + CO2 + H2O
Carbonate decomposition
% Hydrolysis
100
50
10 20 30 40 50 P in bars
REACTION 2 :
Na2CO3 + H2O  2 NaOH + CO2
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
Oxygen scavengers
MAIN OXYGEN SCAVENGERS
 sulfites :
Na2SO3 + ½ O2
 hydrazine :
N2H4 + O2
 tanins
Na2SO4
N2+H2O
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
3
3
2
2
1
1. Adsorption
1
2. Ion - ion
3. Hydrophobic bond
PSEUDO-COMPLEX
FORMATION
CH3
CH3
CH2 CH2
N
H
O
H
Fe
O
O
CH2 CH2
N
O
H
H
Fe
O
O
H
H
Fe
H
Fe
H
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
Potentiostat
I
Auxiliary
electrode
(Pt)
mA
mV
E
Reference
electrode
Rotating disc
electrode (steel)
IMPEDANCE DIAGRAM
- jG (.cm2)
HF loop :
film evidence
R (.cm2)
Re
Rp
Cd
Cd
Re
CHF
Re
Rp
Rp
RHF
Protection of boiler
tubes
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.

Magnetite production :
experimental procedure
Emulsion water/steam 24 %
H2
Incondensable
gases
Expansion
condensation
cooling
Boiler
tube :
 = 23 w/cm2
P = 100 bars
T°C = 315 °C
Make - up :
demineralized
water
3 Fe + 4 H2O
 Fe O
3
Shikorr reaction
4
+ H2
Stability of the magnetite layer
H2 as vpm (volume per million)
Magnetite production
POLYAMINE injection
10
2 vpm during 72 hours
2
time
HEAT EXCHANGE
The polyamine film formed
on metal surfaces does not affect
the thermal exchange.
 Presence of polyamines
increases the yield of condensers.

THERMAL EXCHANGE
 in w/cm.°C
V D.I. water C = 100 ppm C = 1000 ppm
0.5 m/s 0.17
0.167
0.167
1.0 m/s 0.166
0.166
0.166
1.5 m/s 0.165
0.165
0.165
DROP CONDENSATION
Dh (%)
5
Film condensation
4
3
2
1
ppm ODA
Drop condensation
0
1
2
3
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
