Refractory failure analysis-K.P.PRADEEP KUMAR

Refractory failure at Tip casting area

Castable should be heatedvery carefully to control thesteam presure

ACW 1&2 - Picture before bursting

Castable bursted due toun controlled steam pressure ,11 hr after initial heat-up

(ACW)

Castable bursted due to uncontrolled steam pressure . This was due to 1) rapid heating as the flame was much shorter . Pilot burner- oil flame was close to the outlet and the castable. 2) Oil spilled on the castable and caused local heating.

Castable burstedat nose ring area

ACW 1 & 2

It is observed that only castableblocks at the bottom half got damaged more.

Castable failure at the tip casting area at ACW

Causes:(at the time of heating up kiln ,after major lining)

• too short oil flame close to the castable causeduncontrolled steam pressure resulted in bursting of castable.

• oil spillage on the castable caused local heating

Remedies• Elongate the flame and push the burner farther inside the kiln so

that radiation Is reduced on the castable.• Spread clinker nodules on the refractories from tip to 10 M length • Changed over to andalusite based castable.

APCW

cracks begin , after one month Operation at the junction of twomonolithic blocks

This crack formation is due to Inadequate expansion joint aftertwo months of kiln operation. Thereis no wear but observed cracks on the Surface and deep cracks at the junctionOf two castings.

APCW

Castable failure after 4 months operationdue to inadequate expansion joint andThermal shocks

APCW

Castable failure due to Inadequate expansion joint causesdeep crack formation and spallingafter 4 months of operation.

APCW

Deep penetration of clinker liquid Into the brick.

One monolithic casting has crossed to the other casting and the blocks expandedtaking the casting along with, whichended in spalling.There should be a clear expansion joint of 10 mm betweenthe blocks.

APCW

Remedies

• Tip casting plates( with male and female joint) have been modified to straight blocks .

• Castable was changed from andalusite based to Corundum based to withstand abrasion.

• Expansion gap was increased from 5 mm 15 mm with ceramicboards

Refractory failure on the tip casting at APCW

Causes

• Thermal shocks • Cracking due to inadequate expansion joint . ( expansion joint closed

during vibration) Very often it is observed that the expansion gapbetween the castings are filled with Castable.

This L –joint will not allowto give expansion joint properlly( overlapping dueto male and female joint

Before modification

This straight expansion jointallows proper expansion.

After modification

Castable on the modified blocks APCW

Expansion joint is straight in the Modified castings.

Tip casting blocks are not in lineThis V-joint will make make the brickring mis aligned. The suppliers engrave the letters on the castings on the collar which makes point contactwith the bricks. It can be engraved on the on the hot face side.Dimension tolerance must not deviate from limit specified by OEM.

AC kiln

Tip castingRetainer ring

a

b

c

d

e

a

b

c

d

e

Tip casting Retainer ring

A=b=c=d=e and so on a,<b =c < d=> e

Installation of castings at the kiln tip area.

Casting’s periphery at its base side must be in line.

.

.

Nose ring Blocks

Suppliers must be advised not to engrave the letters on the baseand the collar where bricks have contact with castings.

Letters can be engraved on the hot face ofthe castings

Bolts must never beprotruded .This acts like a pivot and castingswill not have contact withthe bricks. Casting must have machined surfaceand the blurs must beground to get fine surfaceon the castings..

Engraved letters and blurs can createpoint contact between the bricks and the castings which will pinch the brick surfaceand causes refractory failure at the tip.

Ensure 100 % contact betweenThe brick and the castings

Nose ring castings

Engraved letters and blurs can createpoint contact between the bricks and the castings which will pinch the brick surfaceand causes refractory failure at the tip.

Ensure 100 % contact betweenThe brick and the castings

Nose ring castings

HA-70 bricks twisted at 47 m

Castings got oxidisedas well as corroded

V-joint gap due to bell mouthOr casting got sunk. If castingface is not smooth it can create this gap. This need a machined Surface. Point contact is notacceptable. Letters engraved on theface can also create gap because of point contact.

AC

Bell mouth formation atKiln outlet

AC

Casting are oxidised tooAfter 3 months of operationThinned down to almost half.

This V gap formation is due to bell mouth formation.

AC

AC

Bricks got crushed The bricks on the retainerring were pushed by20 – 30 mm. That timethe kiln had severeUpset run. Huge variationin chemistry , due toLow silo level and flux variation due to wetness of red ochre.

0 –1.2 M area

The bricks are crushedDue to excessive thrust.Bell mouth formation is also there.

VC-3 Kiln

The castings are oxidized as well as corroded after 3 months of operation. When we fire pet coke Nickel/ chromium Ratio needs change .Also found that there is wear though the hard face welding is done. High Efficiency cooler increases the secondary temperature and may burn the castings .The dust erosion and clinker falling on the Castings can also increase the wear .Nosering cooling must be enhanced. Cooling air volume =400 Cum/min , and velocityof air at nozzle t >45 M/s and the no.of nozzles , minimum is 6.

RC-3 Kiln

The gap created must be due to bell mouth Formation or nose ring castings got sunk because of intolerable heat.Nose ring cooling must be enhanced

RC3 Kiln

Out let blocks are crackedDue to over heating after the Installation of high efficiencyStatic grates cooler.

GS Kiln

Now the hot face is covered byCastble.The life has increased to more than one year.

GS Kiln

Nose ring cooling

For kiln Dia < 4.0 M, cooling air volume 400 cum/min

For kiln dia > 4.0 M, cooling air volume 500 cu m/ min

Nozzle velocity = 40 – 45 m/s

Minimum no.of nozzles =6< 1.5 M

0 –2.2 MVC-3 Kiln2 nd row after tip casting

Unstable coating due to high sulfur recycle variationLow alumina modulus. High liquid forms the coating uptothe tip. Sufur volatile factor some times reach > 3.5 and Varied from 2 to 3.5.Petcoke sulfur exceeds 7.5%.

Refractory failures at the tip castingin AC and VC

Causes• bell mouth formation• Casting loose their mechanical stability due to corrosion and

oxidised• Insufficient cooling of nose ring• Frequent ring formation and doslodgement at the tip and

consequent thermal shocks• High liquid content and variation in clinker liquid quality due to

variation in sulfur cycle.Often it crossed > 3.0 .

Remedies• change the outlet shell• Improve the nose ring cooling air volume and cooling nozzle velocity• Control the chemistry and sulfur cycle.• Nickel / Chromium has to be adjusted as Nickel is vulnerable to sulfur

attack and chromium to alkali attack.

This is due to bell mouth formation. Even the spinel bricks had failed. Mortarapplication is must to have more flexibility.

VC-3 Kiln

0 –2.0 M

Bricks on the retainer ringgot crushed

VC-3 Kiln

Even the bricks on the retainer ringgot shifted due to excessive axial thrustSudden increase in temperature on brick surfaceDue to coating collapse. kiln had severe upset run When this failure occurred.

AC kiln

Refractory failure at retainer ring area in AC and VC.

Causes• instability of coating in this area due to change in chemistry and variation in sulfur

cycle because of petcoke firing• Excessive axial thrust due to higher vrpm• Flame needs tuning • Rhino horn formation on burner tip distorts the flame.

Remedies• Variation in chemistry needs control • Higher grade spinel bricks will improve the life• flame should be shaped to short , convergent and hot flame.• Install shock blasters to dislodge the Rhino horn on the burner tip.

30 % of the brick is penetrated .Aggressive liquid attack on brick ( 33 % liquid inclinker)

These cracks show that the bricks undergone severe thermo-mechanical Stresses.

APCWLocation : 1st row after tip casting block.

The gap between the castings is much higherthan the OEM specifications.

Deep penetration of liquid into the bricks

Theses crack show that there is severe stresses onthe bricks Thermo-mechanical as well as thermo chemical( bell mouth formation and aggressive liquid attack on the brick)

APCW

Refractory failure at kiln outlet – APCW

Causes;• Too high liquid % which penetrate deep into even the spinel bricks and

degenerate spinels and destruct the bricks. Coating is also unstable • Bell mouth formation causes thermo-mechanical stresses• Casting are not in line as their dimensions have deviation than the

tolerance limits than specified by OEM.• axial thrust

Remedies• Optimize the liquid to reduce coating• Castings must have tolerance limit as recommended by OEM• Change the outlet cone shell to straight shell to reduce the axial thrust with• installation of conical retainer rings of Magattoux.

GCWEven the spinel bricks had beenImpenetrated by aggressive liquidDegenerate the spinels . The bricks losses Its strength.

GCW

GCW

GCW

GCW

Hasle D-59 A castable

Bricks are twistedand crushed due to high axial thrust

GCW-1

If bricks are attacked by aggressive liquid they are vulnerable to any stresses

Failed area adjacent to retainer ring

GCW-1

Shell surface is rough We have to apply mortarUnderneath the bricks .to have full contact with the shelland cold face of the brick.

GCW-1

GCW-1The spinel bricks are crushedand destructed

up to half of the brick thickness is attacked by aggressive liquid attack.

GCW-1

Deep melt infiltration insideThe brick. The bricks had undergoneVery high thermo- chemicalAnd thermo mechanical load.

Almost 50 % brick is attacked by liquidWhich can destroy the ingrediants of thebrick . This is a hercynite Spinel brick , Ankral Z1.

GCW-1

Huge cracks showthe bricks undergoneSeverer thermo-mechanicalstresses. The Thermochemical attack on the bricks make more vulnerable for thermo-mechanical stresses

GCW

Refractory failure at kiln outlet – GCW

Remedies• High grade spinel bricks which only increases the life by giving

resistance to aggressive liquid attack. Variation in quartz has to be reduced.

• Replacement of conical shell to straight shell to reduce axial thrust. Conical retainer ring is the second option to arrest the thrust.

• Live ring migration at first tyre must not be more than 12mm/revolution.Proper shimming has to be done accordingly.

• Surge hopper has to be installed to collect the bag house dust to reduce chemistry variation in kiln feed.

Causes Very high burning zone temperature due to presence of quartz and to maintainfree lime < 1.1 %. The liquid has less viscosity and penetrate the bricks deep.changes in chemistry when raw meal stops , variation in kiln feed LSF by 2-4Flame gets distorted often due to rhino-horn formation on burner tip very high variation in I tyre migration due to coating instability , ie 0 mm to 30 mm

Refractory failure atretainer ring area - APCWand GCW kiln

APCW Bricks got crushed at the retainer ring

Bricks at the retainer ring gotCrushed due to excessive axial thrust. Very high thermo-chemicalStresses on the bricks. Liquid

had deep penetration and destructedthe spinels and The texture.of the bricks.

Crushing of the bricks

APCW

Bricks crushed at theRetainer ring

Refractory failure at kiln outlet and near the retainer ring – APCW and GCW.

ReasonsFrequent coating failure due chemistry variationToo high liquid % in clinker ie.,33%Flame and reduced conditionsSevere thermal shocks due to coating dislodgement which takes awaypart of the bricks.

RemediesOptimise the liquidChange over to high grade spinel bricks like Almag AF or Ankral R1Due to dusty conditions flame gets disturbed and reduced conditionsprevail . This causes the coating very unstable and causing thermal Shocks.

Too many retainer rings are unneceassryThey act like stiffeners and when kiln shell getsHeated up this will, shear the shell . 75 mm thickRetainer ring is tougher than kiln shell. Therer are4 rows of Magattoux retainer rings from 1.2 – 1.8 Meter ,double retainer ring at 1 M and Single retainer ring.at 0.4 M

Shell is warped at many places

Bricks are under stress

Alumina bricks is a not good selectionThe conical retainer ring are meant forSpinel bricks

HCW

Bricks have cracks Shows that bricks are underThermo mechanical stress.First row bricks are totally crushedand washed out. The castable alsogot dislodged as the brick ring movedand created axial thrust on the castable too. The second and other ringsmoved forward by 45 mm.

Shell crack axial

Retainer ring surface is wavy

Retainer ring is burnt.

Shell crack ,

Retainer ring crack

Shell crack

crack onretainer

Conical retainer ring ofRHI & Magattoux

Surface is wavy

Castable casted onthe tipcasting face ,doneat site

First retainer ring warped. This makes the bricks twisting .

As the shell is having wavy surface the conical retainer ring donot have contact surface with bricks and hence bricks need cutting at the bottom by 12- 18 mm in many places andmortar application underneath the bricks to fill up the gaps.Mortar application is done at radial joints too.

After conical rings no extra retainer ring is needed

Refractory failure at retainer ring area HCW

RemediesDamaged outlet shell is to be replaced by new shellSpinel bricks will be used on the conical retainer ring instead of High alumina bricks to have better locking and arching which avoids shifting.Retainer ring must have smooth surface and have the same curvature of kiln.After conical retainer ring no retainer ring is needed as recommended by refractory suppliers

Causeswrong selection of brickstoo may retainer ringsshell surface is wavy and warped also.conical retainer rings are not fixed properly as it is observed that it falls at 12 O’ clock position while rotating the kiln

Thanks a lot

PRADEEP KUMAR