Some Basics on Corrosion...8 Basics on Corrosion in WtE-Plants CheMin Prewin General Assembly at...

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

Thinking about corrosion

Fluegas (solid, liquid, gaseous matter)

Heat Materials, permeable for heat,

...but not for matter

Chemical components on the surface of tube material

Fluegas

Fouling/ Deposits

Corrosion

matter (solid, liq., gas)heat

matterheat

corrosion

...own system,maybe even encapsuled

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

...barriers by materials or gap“

...minimize? ...what? use monitoring!

...chose e.g. conversion in flue gas, moderate heat transfer etc.

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)

KBrNaBrNaClKClCaBr2CaCl2

width 6 mm

Corrosion rate

0.5 to 1 mm per 1000 h

Thermodynamics in terms of vapor pressure

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

Mild steel Cladding HVOF (therm. spray coat.)

Barrier materials: Saltmelt corrosion (SH 400°C)

Concept of „No chemical gradient“:

Barrier without contact to the tube surface (as explained for „no thermal gradient“)

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

no additive

SO3-injection

in full-scale test

48h operation

65h operation

corrosion

Corrosion: Influence of chemical gradients (avoid chlorids by sulphation)

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

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, 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

CheMin

Heatflux measurement - Corrosion monitoring

Thomas Herzog, Hans-Peter Aleßio, Wolfgang Spiegel & Gabi Magel

Thinking about corrosion

Fluegas (solid, liquid, gaseous matter)

Heat Materials, permeable for heat,

...but not for matter

Fluegas

Fouling/ Deposits

Corrosion

is matter (solid, liquid, gas)and heat

matterheat

corrosion

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

Corrosion rate depends on temperature of tube material

Corrosion: Influence of temperature on the alloy

Arrhenius (energy of activation)

Boßmann & Singheiser 1996

Material (‚more cold‘)

Fluegas (‚more hot‘)

Corrosion

Maturing:Chloridessend outcorrosivechlorine

gradient

Corrosion,

increases local temperatures

Fluegas unsteady,

increases local temperatures

Fouling, corrosion and temperatures

width 3 mm

Kalium-Fracht

EBSBiomasse MVA

Potassium loads (particles/ condensed) in fluegas

7 Biomass plants 3 RDF plants 6 W-t-e plants

Blei-Fracht

EBSBiomasse MVA

Lead loads (particles/ condensed) in fluegas

7 Biomass plants 3 RDF plants 6 W-t-e plants

Bleichlorid

200250300350400450500RG-Temperatur [°C]

PbCl2 im RG löslichin Rauchgaspartikeln

1E-4 bar

1E-5 bar

1E-6 bar

Kaliumchlorid

200250300350400450500550600650700750800

RG-Temperatur [°C]

KCl im RG löslichin Rauchgaspartikeln

1E-4 bar

1E-5 bar

Corrosion: Saturation in flue gas increases during cooling

400°C critical on SH and in deposits on evaporator

Particles formed in flue gas

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

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

Prewin General Assembly at Goslar, Germany, June 2010W

DepositWat

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

2 3 4 5 6 7 8 9 10 11 12

dT Rohr-Steg [K]

16.11.08 17.11.08 18.11.08 19.11.08 20.11.08

t [Tage]

Corrosion: Influence of thermal gradients caused by heat flux

Heat flux: Pattern of „less hot“ and „more hot“ regions on tubewalls

269°C

272°C

250°C

263°C

271°C

measured calculated

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

109 103

101LSW RSW

dT Seitenwände

Nov. 08 Dez. 08 Jan. 09 Feb. 09 Mrz. 09 Apr. 09 Mai. 09 Jun. 09 Jul. 09

t [Tage]

109 111

dT Seitenwände

t [Tage]

103 101

dT Seitenwände

t [Tage]

109 103

dT Seitenwände

t [Tage]

111 101

Corrosion: Detect and correct disbalance in flue gas stream

...control and adjustment to bring in operation or to approve operation

Heat flux measurements: Development or cycles of fouling

Boiler temperature and steam load

Tube-fin-temperature differences

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

Some Basics on Corrosion...8 Basics on Corrosion in WtE-Plants CheMin Prewin General Assembly at...

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