Kiln Shell Corrosion

Kiln Shell Corrosion

Cement

ICTM • R. Krischanitz • May 2008

29 Kiln Shell Corrosion

PC kiln, Ø 4.15 x 58 m, 2450 tpd, <20% alternative fuels:

Fracture of kiln shell at rm 38.5 - despite phosphating it during previous kiln stops

Kiln shell thickness:

Original thickness 20mm

Thickness within fracture area (groove) 8mm

Average thickness in brick joints 14mm

Thickness below bricks 17mm

Ref: DAVILA, J.C. et al., 1995, Influencia del Refractario en la Corrosion de la Coraza del Horno Rotatorio para Cemento, ALAFAR XXIV Congreso, Cartagena, pp 157-183

Fracture of kiln shell due to corrosion

3 29 Kiln Shell Corrosion

Preferred corrosion below joints, condensation of moisture during kiln stops

Corrosion of kiln shell (rm. 65, calcining zone)


wet cardboards

Corroded kiln shell within the calcining zone


Loss of shell thickness 6 mm/a

Fuels: Coal + pet coke, tyres, palletised sewage sludge

Kiln shell corrosion (rm. 29, second tyre)


Thickness15 mm

Scales from the kiln shell


© RHI Technical Centre Leoben, Austria

Dense layer of magnetite and hematite

mag

hem

Porous layer of hematite and KCl

hem

KCl

Microscopical appearances of scales


Composition of scales6DPSOH A B C D E F G

Fe2O3 44 90 88 17 56 n.a. 81

SO3 11 7 5 1 1 -

K2O 24 - 2 43 16 6

Na2O 4 - - - 2 1

Cl- 6 1 4 36 11 6

F- 7 - - - - -

PbO - - 1 - - -

Fe3O4 [[[ [[[ [ [[ [[[ [[

Fe2O3 [[[ [ [[ [[[

FeS [[ [[ [ [ [[

FeS2 [[

Fe(OH)2 [

FeSO4.H2O [

K2SO4 [[

KCl [[ [ [[[ [[ [[ [[

Na2SO4 [ [

NaCl [

NaF [

Pb2(SO4)O [

&KHPLFDO�DQDO\VLV�(wt.%)

0LQHUDO�3KDVHV��;5'�


Kiln Feed / Coating

Kiln gas

KCl, K2SO4KCl, K2SO4

KCl, K2SO4 KCl, K2SO4

Preheater

/LQLQJ

Evaporation of volatiles in preheating zone


Lower melting points of chlorides in comparison to sulphates. Eutectic melts have even lower melting points. The lower the melting point the higher the infiltration depth.Phase diagram: acc. to O.S.Dombrovskaya 1933

Phase diagram KCl – K2SO4


Spalling of basic bricks caused by KCl after 3 months operation

Infiltrated refractory bricks


� Reduce chlorine input to the kiln (selection of appropriate raw materials / substitute fuels, install a by-pass)

� Keep evaporation rate of volatile components as low as possible (avoid reducing operation conditions, use of mineralizers, other process measures)

� Reduce permeability of lining (e.g. reduction of joints by use of ISO shapes in the basic zone, use of mortar lining)

� Extension of the basic lining area

� Install refractories with low (zero) permeability

� Apply gas-tight coatings on the kiln shell (paints, flame / plasma sprayedmetallic or ceramic layers etc.)

� Select corrosion resistant steel type for kiln shell

� Sacrifice layercf also: Jøns, E.S. & Østergård, 1999, Investigation into kiln shell corrosion of rotary cement kilns, ZKG International,

vol. 52, No. 2, pp. 68-79

Measures to prevent kiln shell corrosion


� Heat resistant up to 400°C

� Chemical resistance against alkaline salts

� Chemical resistance against corrosive gases (H2S, HCl, SO2, CO2 and O2)

� Resistance against acids

� Abrasion resistant (movement of the lining)

� Coating must be applicable on sight

Requirements for coatings


Materials tested by University of Leoben / RHID. Jellen: “Verringerung der Ofenmantelkorrosion von Drehrohröfen in der Zementindustrie durch Beschichtungen”

� 3DLQWLQJV: - polyamide resin with graphite pigments- silicon resin with FeO pigments and inhibitors- silicon-modified alkyd resin- zinc ethyl silicate- phosphoric acid

� 0HWDOOLF�FRDWLQJ, flame sprayed: - Al- NiCr 50/50 - Ni based Cr-B- Zn, Zn/Al 85/15

� &HUDPLF�FRDWLQJ, plasma sprayed: - Al2O3

Studied types of coating


� Ignition test at 400°C:

kiln atmosphere: CO2 20%H2O 10% SO2 2%HCl 2% O2 13%N2 53%

additionally the specimens were coated with alkaline-salts

� Low temperature corrosion:at 40°C in an exsiccator which base has been covered with HCl (21%)

Weight differences were measured over a longer period of time (up to1000 h)

Performed tests


� Paintings: embrittlement occurs at moderate temperatures (e.g. 200°C),loss of adhesion on substrate

� Phosphate treatment guarantees no protection against corrosion at hightemperatures. After the ignition tests no phosphate detectable anymore.

� Metallic coating: protective effect is good / very good (e.g. Al) but adhesion on substrate is difficult to maintain

� Ceramic coating: high porosity of the ceramic layer leads to corrosion of the substrate and finally spalling of coating

Spray procedure expensive and time consuming (14 days one layer 5rm, 3,8m �), rough surface – difficult to clean from mortar

Results of investigation


Fused cast refractories

• Zero permeability

• Very expensive

• Very brittle / low thermal shock resistance

Silica-impregnated alumina bricks (RESISTAL IS)

• Reduced open porosity (15-20% less porosity)

• Greatly reduced permeability (80-90% less permeability)

• Formation of protective reaction layer of alkali silicates at hot face („reaction sealing“)

Refractories with low (zero) permeability


What is a sacrifice layer?

Method developed in Mexican cement plants („lamina de sacrificio“)

A sheet of stainless steel between refractory lining and kiln shell

Steel type: 1.4301 (AISI 304), 1.4571 (AISI 316)

Dimension: (A) 900 mm wide endless coil, 0.38 mm thickness, or (B) 1.220 x 2.440 mm, 0.79 mm thickness, point welded

Sacrifice layer against kiln shell corrosion


900 mm wide endless coil, 0.38 mm thickness

Sacrifice layer (A)


Type of steel used for sacrifice layer

Sacrifice layer (A)


Cutting pieces of 2-3 m length

Sacrifice layer (A)


Four sheets ready for installation

Sacrifice layer (A)


SL installed between ANKRAL bricks and the cleaned kiln shell

Sacrifice layer (A)


Sacrifice layer (A)


Plates of 0.79 mm thickness are point welded to the kiln shell

Sacrifice layer (B)


Sacrifice layer (C)

vertical overlap: 2 – 5cmhorizontal overlap: 5 – 20cm

magnetswooden bar

refractory bricks

stainless steel sheets 1.4301 / AISI 3040,40 x 1000mm

lining rig

Stage 1 Stage 2


Steel shell with sacrifice layer (rm 30-35): very light corrosion

Steel shell without sacrifice layer (rm 52): strong corrosion

Fuel: Combustóleo + alternative fuels (PET, tyres, industrial waste)

Effect of sacrifice layer in a PREPOL kilnØ 4.8 x 75m, 4.800 tpd


� Davila, J.C. et al., 1995, Influencia del Refractario en la Corrosion de la Coraza del Horno Rotatorio para Cemento, ALAFAR XXIV Congreso, Cartagena, pp 157-183

� Jøns, E.S. & Østergård, 1999, Investigation into kiln shell corrosion of rotary cementkilns, ZKG International, vol. 52, No. 2, pp. 68-79

� Jellen, D., 1999, Verringerung der Ofenmantelkorrosion von Drehrohröfen in der Zementindustrie durch Beschichtungen. Thesis, Montanuniversität Leoben.

References


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Thank you for your attention!

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Kiln Shell Corrosion