Some Basics on Corrosion...8 Basics on Corrosion in WtE-Plants CheMin Prewin General Assembly at...
Transcript of Some Basics on Corrosion...8 Basics on Corrosion in WtE-Plants CheMin Prewin General Assembly at...
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Corrosion in Waste-to-Energy Plants
Some Basics on Corrosion...and the Effect of Heatflux (see Part 2 of Presentation)
Thomas Herzog and Wolfgang SpiegelCheMin GmbH, Augsburg
www.chemin.de
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Thinking about corrosion
Fluegas (solid, liquid, gaseous matter)
Heat Materials, permeable for heat,
...but not for matter
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Chemical components on the surface of tube material
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Chemical components on the surface of tube material
Tube
Fluegas
Fouling/ Deposits
Corrosion
matter (solid, liq., gas)heat
matterheat
corrosion
°C
...own system,maybe even encapsuled
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Specific questions:
• Is it possible to have no aggressive chemical components in the flue gas?
...if not possible:
• Is it possible to keep away aggressive chemical components from thetube?
...if not possible:
• Is it possible to minimize the aggressivity of the chemical components on the tubes?
Thinking about corrosion, corrosion protection, corrosion minimization
NO!
...barriers by materials or gap“
...minimize? ...what? use monitoring!
...chose e.g. conversion in flue gas, moderate heat transfer etc.
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Corrosion happens due to reaction with gaseous species or liquids of salts
Corrosion: Influence of aggressive chemical components
In „conventional“ WtE-Plants chlorine species is the mainaggressive chemical component (...do not underestimateoxygene (...re-passivation, scaling) or sulphur (...SH >400°C)
Almost all corrosion mechanism are connected to salts of chlorides:
• Thermodynamics in terms of solubility
• Thermodynamics in terms of vapor pressure
• Thermodynamics in terms of solid to liquid
Sättigungskonzentration ausgewählter Halogenide(SGTE-Daten)
1,0E-03
1,0E-02
1,0E-01
1,0E+00
1,0E+01
1,0E+02
1,0E+03
1,0E+04
1,0E+05
1,0E+06
1,0E+07
50 150 250 350 450 550 650 750 850 950 1050 1150 1250 1350
Temperatur (°C)
Geh
alt (
mg/
m³)
KBrNaBrNaClKClCaBr2CaCl2
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
width 6 mm
Corrosion rate
0.5 to 1 mm per 1000 h
Thermodynamics in terms of vapor pressure
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Mass transfer (a path towards the corrosion front for the aggressive agent)
Concept of barriers
The barrier has to be:
• Not permeable for gases
• Sufficient for the designed heat transfer
• Resistant against corrosion potential similar or better than the tube alloy
• Sufficient thermal and mechanical properties (strain, erosion)
Corrosion: Influence of mass transfer towards the tube surface
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Mild steel Cladding HVOF (therm. spray coat.)
Barrier materials: Saltmelt corrosion (SH 400°C)
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Concept of „No chemical gradient“:
Barrier without contact to the tube surface (as explained for „no thermal gradient“)
Or:
Transfer of all aggressive chemical components in the fouling towards„inert“, stable phases (no chlorides).
This is attempted by additives (i.e. sulphation)
Corrosion: Influence of chemical gradients
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
no additive
SO3-injection
in full-scale test
48h operation
Iron
Iron
65h operation
corrosion
corrosion
Corrosion: Influence of chemical gradients (avoid chlorids by sulphation)
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Concept of „No thermal gradient“:
Barrier without contact to the tube surface.
For example ceramic plates (rear ventilated plates)
The ceramic transfers heat by radiation like a chemically „clean“ flue gas
The hot surface of ceramics do not act as cooling trap
No salts in the fouling
Corrosion: Influence of thermal gradients
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
If the concept of „no thermal gradient“ is not possible:
Shallow thermal gradient (in fouling, corrosion products etc.):
Limited heat flux (KW/m2)
A shallow thermal gradient can be achieved by boiler design
Corrosion: Influence of thermal gradients
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Corrosion, corrosion minimization:
• Firing conditions ...conversion from fuel to fluegas and fouling
• Design of boiler and firing ...thermal and chemical gradients
• Fluegas and fouling conversion ...addititves
• Time-temperature-turbulence
• Materials ...ceramics and alloys
Corrosion: Some keywords and key-issues
Corrosion monitoring:
• Only useful in a concept of „Early Recognition of Corrosion“ ...ahead of problems and damage
• Yearly, monthly, weekly, daily checks to monitor drifts
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
CheMin
Heatflux measurement - Corrosion monitoring
Thomas Herzog, Hans-Peter Aleßio, Wolfgang Spiegel & Gabi Magel
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Thinking about corrosion
Fluegas (solid, liquid, gaseous matter)
Heat Materials, permeable for heat,
...but not for matter
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Chemical components on the surface of tube material
Tube
Fluegas
Fouling/ Deposits
Corrosion
is matter (solid, liquid, gas)and heat
matterheat
corrosion
°C
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Strength: Maximum temperature for alloys
Thermal segregation in Ni-base alloys:...starts approx. >600°C in cladding with alloy 625...starts approx. >500-550°C in thermal spray coatings with alloy similar 625 (+B +Si)
Live steam 465°C Biomass 500°C Waste
450
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Corrosion rate depends on temperature of tube material
Corrosion: Influence of temperature on the alloy
Arrhenius (energy of activation)
Boßmann & Singheiser 1996
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Material (‚more cold‘)
Fluegas (‚more hot‘)
Corrosion
Maturing:Chloridessend outcorrosivechlorine
gradient
gradient
Corrosion,
increases local temperatures
Fluegas unsteady,
increases local temperatures
Fouling, corrosion and temperatures
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
width 3 mm
Thermodynamics in terms of vapor pressure
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Fe
S Cl
Na K
Zn Pb
Thermodynamics in terms of vapor pressure
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Kalium-Fracht
0
100
200
300
400
500
600
[mg/
Nm
³]
EBSBiomasse MVA
Potassium loads (particles/ condensed) in fluegas
7 Biomass plants 3 RDF plants 6 W-t-e plants
Corrosion: Influence of aggressive chemical components
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Blei-Fracht
0
20
40
60
80
100
120
140
160
[mg/
Nm
³]
EBSBiomasse MVA
Lead loads (particles/ condensed) in fluegas
7 Biomass plants 3 RDF plants 6 W-t-e plants
Corrosion: Influence of aggressive chemical components
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Bleichlorid
0,001
0,01
0,1
1
10
200250300350400450500RG-Temperatur [°C]
[g/N
m3]
PbCl2 im RG löslichin Rauchgaspartikeln
1E-4 bar
1E-5 bar
1E-6 bar
SMP
Kaliumchlorid
0,001
0,01
0,1
1
10
200250300350400450500550600650700750800
RG-Temperatur [°C]
[g/N
m3]
KCl im RG löslichin Rauchgaspartikeln
1E-4 bar
1E-5 bar
SMP
Corrosion: Saturation in flue gas increases during cooling
400°C critical on SH and in deposits on evaporator
Particles formed in flue gas
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Saltmelt formation and high availability of chlorine gas (vapor pressure)
e.g. around400°C is a critical zonein the systempotassium-lead-chloride 230-300°C
criticalzone
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Corrosion front, e.g. 280°C
Flue gas side
Distance of chlorides fromthe corrosion front and
activity (vapour pressure) depends on heat flux
Lead-Potassium-Chloride
„Feels fine“ at about400°C
Ironchloride width 1,5 mm
Corrosion: Influence of thermal gradients caused by heat flux
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010W
ater
-ste
am
Tube
DepositWat
er-s
team
Tube
Szenario B:=lower heat flux=flat gradient
Deposit
Szenario A:=higher heat flux=steep gradient
Szenario A:=smaller distance to tube=higher corrosion dynamic
Szenario B:=higher distance to tube=lower corrosion dynamic
400°C-Isotherme=favouritelead chloride zone
250°C
650°C
250°C
450°C
Corrosion: Influence of thermal gradients
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
2 3 4 5 6 7 8 9 10 11 12
dT Rohr-Steg [K]
Abze
hrun
g [m
m /
1000
h]
0
5
10
15
16.11.08 17.11.08 18.11.08 19.11.08 20.11.08
t [Tage]
[K]
Corrosion: Influence of thermal gradients caused by heat flux
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Heat flux: Pattern of „less hot“ and „more hot“ regions on tubewalls
269°C
272°C
250°C
250°C
263°C
271°C
measured calculated
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Measurement of temperature differences (<0,1 K) at a high temperature level (240 - 300°C)
Temperature difference induces thermoelectric effect, Seebeck-Effect
Literature: Sascha Krüger (2009)
Heat flux: Measurement
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
111
109 103
101LSW RSW
FW
dT Seitenwände
0
5
10
15
Nov. 08 Dez. 08 Jan. 09 Feb. 09 Mrz. 09 Apr. 09 Mai. 09 Jun. 09 Jul. 09
t [Tage]
[K]
109 111
dT Seitenwände
0
5
10
15
Nov. 08 Dez. 08 Jan. 09 Feb. 09 Mrz. 09 Apr. 09 Mai. 09 Jun. 09 Jul. 09
t [Tage]
[K]
103 101
dT Seitenwände
0
5
10
15
Nov. 08 Dez. 08 Jan. 09 Feb. 09 Mrz. 09 Apr. 09 Mai. 09 Jun. 09 Jul. 09
t [Tage]
[K]
109 103
dT Seitenwände
0
5
10
15
Nov. 08 Dez. 08 Jan. 09 Feb. 09 Mrz. 09 Apr. 09 Mai. 09 Jun. 09 Jul. 09
t [Tage]
[K]
111 101
Corrosion: Detect and correct disbalance in flue gas stream
...control and adjustment to bring in operation or to approve operation
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Heat flux measurements: Development or cycles of fouling
Boiler temperature and steam load
Tube-fin-temperature differences
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CheMinBasics on Corrosion in WtE-Plants
Prewin General Assembly at Goslar, Germany, June 2010
Applications• Operation experiences approve heat flux measurements as cheap measure to
monitor the inside of the boiler from the outside. These must be used in addition
to the conventional monitoring (temperature, HCl, SO2 etc.)
• Disbalances can be visualized reliable and can be balanced (adjust the firing
control)
• Online-cleaning must not be done periodical, but can be done on demand
• Corrosion potentials can be detected
improve availability
Heat flux measurements