Ref failur e analysis tip casting & retainer area f


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Ref failur e analysis tip casting & retainer area f

  1. 1. Refractory failure analysis-K.P.PRADEEP KUMAR
  2. 2. Refractory failure atTip casting area
  3. 3. Castable should be heatedvery carefully to control thesteam presureACW 1&2 - Picture before bursting
  4. 4. Castable bursted due toun controlled steam pressure ,11 hr after initial heat-up(ACW)
  5. 5. Castable bursted due touncontrolled steam pressure . Thiswas due to 1) rapid heating as theflame was much shorter . Pilotburner- oil flame was close to theoutlet and the castable.2) Oil spilled on the castable andcaused local heating.Castable burstedat nose ring areaACW 1 & 2It is observed that only castableblocks at the bottom half gotdamaged more.
  6. 6. Castable failure at the tip casting area at ACWCauses:(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 heatingRemedies• Elongate the flame and push the burner farther inside the kiln sothat radiation Is reduced on the castable.• Spread clinker nodules on the refractories from tip to 10 M length• Changed over to andalusite based castable.
  7. 7. APCWcracks begin , after one monthOperation at the junction of twomonolithic blocks
  8. 8. This crack formation is due toInadequate expansion joint aftertwo months of kiln operation. Thereis no wear but observed cracks on theSurface and deep cracks at the junctionOf two castings.APCW
  9. 9. Castable failure after 4 months operationdue to inadequate expansion joint andThermal shocksAPCW
  10. 10. Castable failure due toInadequate expansion joint causesdeep crack formation and spallingafter 4 months of operation.APCWDeep penetration of clinker liquidInto the brick.
  11. 11. One monolithic casting has crossedto the other casting and the blocks expandedtaking the casting along with, whichended in spalling.There should bea clear expansion joint of 10 mm betweenthe blocks.APCW
  12. 12. Remedies• Tip casting plates( with male and female joint) have been modified tostraight blocks .• Castable was changed from andalusite based toCorundum based to withstand abrasion.• Expansion gap was increased from 5 mm 15 mm with ceramicboardsRefractory failure on the tip casting at APCWCauses• Thermal shocks• Cracking due to inadequate expansion joint . ( expansion joint closedduring vibration) Very often it is observed that the expansion gapbetween the castings are filled with Castable.
  13. 13. This L –jointwill not allowto give expansionjoint properlly( overlapping dueto maleand female jointBefore modification
  14. 14. This straight expansion jointallows proper expansion.Aftermodification
  15. 15. Castable on the modified blocks APCWExpansion joint is straight in theModified castings.
  16. 16. Tip casting blocks are not in lineThis V-joint will make make the brickring mis aligned. The suppliers engrave theletters 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
  17. 17. Tip castingRetainer ringabcdeabcdeTip casting Retainer ringA=b=c=d=e and so on a,<b =c < d=> eInstallation of castings at the kiln tip area.Casting’s periphery at its base side must be in line.
  18. 18. ..Nose ring BlocksSuppliers 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 castingsBolts must never beprotruded .This actslike a pivot and castingswill not have contact withthe bricks. Casting musthave machined surfaceand the blurs must beground to get fine surfaceon the castings..
  19. 19. Engraved letters and blurs can createpoint contact between the bricks and thecastings which will pinch the brick surfaceand causes refractory failure at the tip.Ensure 100 % contact betweenThe brick and the castingsNose ring castings
  20. 20. Engraved letters and blurs can createpoint contact between the bricks and thecastings which will pinch the brick surfaceand causes refractory failure at the tip.Ensure 100 % contact betweenThe brick and the castingsNose ring castings
  21. 21. HA-70 bricks twisted at 47 mCastings got oxidisedas well as corrodedV-joint gap due to bell mouthOr casting got sunk. If castingface is not smooth it can createthis gap. This need a machinedSurface. Point contact is notacceptable. Letters engraved on theface can also create gap becauseof point contact.AC
  22. 22. Bell mouth formation atKiln outletACCasting are oxidised tooAfter 3 months of operationThinned down to almost half.
  23. 23. This V gap formation is due tobell mouth formation.AC
  24. 24. ACBricks got crushedThe bricks on the retainerring were pushed by20 – 30 mm. That timethe kiln had severeUpset run. Huge variationin chemistry , due toLow silo level and fluxvariation due to wetnessof red ochre.
  25. 25. 0 –1.2 M areaThe bricks are crushedDue to excessive thrust.Bell mouth formation is also there.VC-3 Kiln
  26. 26. The castings are oxidized as well as corrodedafter 3 months of operation. When we fire pet coke Nickel/ chromium Ratio needschange .Also found that there is wear though the hard face welding is done. HighEfficiency 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
  27. 27. The gap created must be due to bellmouth Formation or nose ring castingsgot sunk because of intolerable heat.Nose ring cooling must be enhancedRC3 Kiln
  28. 28. Out let blocks are crackedDue to over heating after theInstallation of high efficiencyStatic grates cooler.GS Kiln
  29. 29. Now the hot face is covered byCastble.The life has increased tomore than one year.GS Kiln
  30. 30. Nose ring coolingFor kiln Dia < 4.0 M,cooling air volume 400 cum/minFor kiln dia > 4.0 M,cooling air volume 500 cu m/ minNozzle velocity = 40 – 45 m/sMinimum no.of nozzles =6< 1.5 M
  31. 31. 0 –2.2 MVC-3 Kiln2 nd row after tip castingUnstable coating due to high sulfur recycle variationLow alumina modulus. High liquid forms the coating uptothe tip. Sufur volatile factor some times reach > 3.5 andVaried from 2 to 3.5.Petcoke sulfur exceeds 7.5%.
  32. 32. Refractory failures at the tip castingin AC and VCCauses• bell mouth formation• Casting loose their mechanical stability due to corrosion andoxidised• Insufficient cooling of nose ring• Frequent ring formation and doslodgement at the tip andconsequent thermal shocks• High liquid content and variation in clinker liquid quality due tovariation 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 sulfurattack and chromium to alkali attack.
  33. 33. This is due to bell mouth formation.Even the spinel bricks had failed. Mortarapplication is must to have more flexibility.VC-3 Kiln
  34. 34. 0 –2.0 MBricks on the retainer ringgot crushedVC-3 Kiln
  35. 35. 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 runWhen this failure occurred.AC kiln
  36. 36. 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 sulfurcycle 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.
  37. 37. 30 % of the brick is penetrated .Aggressive liquid attack on brick ( 33 % liquid inclinker)These cracks show that the bricksundergone severe thermo-mechanicalStresses.APCWLocation : 1st row after tip casting block.The gap between the castings is much higherthan the OEM specifications.
  38. 38. Deep penetration of liquid into the bricksTheses 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
  39. 39. Refractory failure at kiln outlet – APCWCauses;• Too high liquid % which penetrate deep into even the spinel bricks anddegenerate 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 thetolerance limits than specified by OEM.• axial thrustRemedies• 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.
  40. 40. GCWEven the spinel bricks had beenImpenetrated by aggressive liquidDegenerate the spinels . The brickslosses Its strength.
  41. 41. GCW
  42. 42. GCW
  43. 43. GCW
  44. 44. GCW
  45. 45. Hasle D-59 A castableBricks are twistedand crushed due tohigh axial thrustGCW-1If bricks are attacked byaggressive liquid they arevulnerable to any stresses
  46. 46. Failed areaadjacent to retainer ringGCW-1
  47. 47. Shell surface is roughWe have to apply mortarUnderneath the bricks .to havefull contact with the shelland cold face of the brick.GCW-1
  48. 48. GCW-1The spinel bricks are crushedand destructed
  49. 49. up to half of the brick thickness isattacked by aggressive liquid attack.GCW-1
  50. 50. 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
  51. 51. Huge cracks showthe bricks undergoneSeverer thermo-mechanicalstresses. The Thermochemical attackon the bricks make more vulnerablefor thermo-mechanical stressesGCW
  52. 52. Refractory failure at kiln outlet – GCWRemedies• High grade spinel bricks which only increases the life by givingresistance to aggressive liquid attack. Variation in quartz has to bereduced.• 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 than12mm/revolution.Proper shimming has to be done accordingly.• Surge hopper has to be installed to collect the bag house dust to reducechemistry variation in kiln feed.CausesVery 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 tipvery high variation in I tyre migration due to coating instability , ie 0 mm to 30 mm
  53. 53. Refractory failure atretainer ring area - APCWand GCW kiln
  54. 54. APCW Bricks got crushed at theretainer ring
  55. 55. Bricks at the retainer ring gotCrushed due to excessive axialthrust. Very high thermo-chemicalStresses on the bricks. Liquidhad deep penetration and destructedthe spinels and The texture.of the bricks.
  56. 56. Crushing of the bricksAPCW
  57. 57. Bricks crushed at theRetainer ring
  58. 58. Refractory failure at kiln outlet and nearthe 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 thermalShocks.
  59. 59. 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 Mand Single retainer 0.4 MShell is warped at many places
  60. 60. Bricks are under stressAlumina bricks is a not good selectionThe conical retainer ring are meant forSpinel bricksHCW
  61. 61. Bricks have cracksShows 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 castabletoo. The second and other ringsmoved forward by 45 mm.
  62. 62. Shell crack axial
  63. 63. Retainer ring surface is wavyRetainer ring is burnt.
  64. 64. Shell crack ,Retainer ring crack
  65. 65. Shell crackcrack onretainerConical retainer ring ofRHI & MagattouxSurface is wavy
  66. 66. Castable casted onthe tipcasting face ,doneat siteFirst retainer ring warped. This makes thebricks twisting .
  67. 67. As the shell is having wavy surface the conical retainer ringdonot have contact surface with bricks and hence bricksneed 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.
  68. 68. After conical rings no extraretainer ring is needed
  69. 69. Refractory failure at retainer ring area HCWRemediesDamaged outlet shell is to be replaced by new shellSpinel bricks will be used on the conical retainer ring instead of Highalumina bricks to have better locking and arching which avoids shifting.Retainer ring must have smooth surface and have the same curvatureof kiln.After conical retainer ring no retainer ring is needed as recommendedby refractory suppliersCauseswrong 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 at12 O’ clock position while rotating the kiln
  70. 70. Thanks a lotPRADEEP KUMAR