Reffailue nosering pradeep kumar
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Refractory failure at nose ring and cooling zoneof kiln
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uncontrollableaxial thrust dueuneven expansionetc
Shell warpageor ovalitybell mouthformation( mechanical stresses)
Wear on refractory due toin- correct selection and wrong installation
In- correct designof retainer rings orwrong location
In adequatespace for expansion
Causes for refractory failure
Thermo-chemicalstresses and thermomechanical stresses
Burning ofcastings
Failure of castables
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Axial thrust and inadequate expansionAxial thrust is always there on the nose ring refractories . This is dueto the inclination of kiln and the expansion of bricks. If refractories cannot withstand they crumble.Though FLS kilns have outlet coneto arrest the thrust in some of the kilns the thrust is still on the nos eringarea. The thrust, due to expansion, can be compensated only giving
extra expansion at the nose ring area.ie between the bricks from nose ring base to retainer ring. If we install bricks in a following way it will reduce the thrust. Some plants placed SS shim on the retainer ring in between two rings of bricks . RHI recommends this method.
4 mm ceramic board on the castingthis is applicable to brick lining too when it is used on tip casting
2 mm SS shim on retainer ring10 to 30 mmceramic pads
2 mm expansion card boardFor alumina bricks no expansion
To be filled with castable.
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Castings burn away now a days, after kiln up gradation and cooler up gradation, because of high secondary temperature, velocity and clinker dust entrainment. If we give castable lining on the hot face side of castings we can increase the life of the castings. Most of the plants face this problems with brick lining on nose ring..
castable2 mm expansioncardboard joints
4mm ceramic board5 mm ceramic boardon the retainerring
Very important is nose ring velocity per nozzle is > 60 m/ sand it should be focused on the casting block not on the kiln shell.Nose ring cooling can be enhanced by intensifying the cooling air jet.
Less tip casting casting life
2 mm Ceramicboards
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to arrest the axial thrust due to extra expansion with ceramicfiber boards can be given. 4mm ceramic fiber boards
( which can withstand1200 deg c) on the casting
5 mm ceramic boardon the retainer ring
2 mm card board
Anchors are of SS310 steal grade with correct spacing
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Axial thrust
1000 mm
198mm198198198178
The brick which is under maximum thrustand stress
300L230230230If we increase the length it maywithstand some more thrust.
Tip shall be alwayscurve shaped
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Nose ring cooling air = 70 m / sWell directed to cool the blocks
5mm ceramic fiber board
Latest tip casting
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Nose ring cooling air is directed on kiln shellthe air is preheated and will not cool the castings- incorrect practice
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Wear on refractory due to in- correct selection and installation
Refractories are to be selected to suit the operational and process conditions . LC castables on Andalusitebased castables are suitable.Corundum based castablesare good wear resistant but they are easily attacked byfree lime and excessive liquid.They are very sensitive to steamformation. Magnesia spinel bricks can take more thermo-Mechanical and thermo-chemical stresses at the nose ring area. Proper expansion is a must to reduce spalling due to expansion. The function of ceramic board is to accommodate the thrust coming from expansion.
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Lack of expansioncauses spalling
GCW
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Inadequate expansion between two monolithic blockscauses this spalling GCW
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Crack formationafter one monthoperation.This is due to inadequateexpansion
APCW
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Castable dislodged from the shelldue to wrong installation .Inadequateexpansion joints caused spalling.The
life is only 3 months
Initial cracksafter 1 month of operation
APCW
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In sufficient expansionjoint at the junction oftwo blocks. Minimum5 mm expansion joint
Is necessary
APCW
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Expansion not givenproperly
Spalling has startedafter one month’s operation
APCW
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Dense surfacedue to more compaction due to
excessive vibration which does notallow the steam escape.
(ACW)
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Castable bursts due toun controlled steam pressure ,11 hr after initial heat-up
(ACW)
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Castable bursts due to uncontrolled steam pressure . This is due to 1) rapid heating as the flame is much shorter 2) too much vibration hence the fines got segregated and close the capillaries 3) absence of organic fibers which burns out to form capillaries 4) It is corundum based castable , needs more water addition and hence very sensitive to the above mentioned reasons. 5) Absence of deflocculants reduce the workability and needs more vibration than needed. Ageing can reduce the effectiveness of deflocculants.
Steam explosion
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Mechanical stresses on the refractories
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Shear cracks due to excessive thrust on bricks adjacent to tip casting
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Liquid infiltration into the brick and damage the bricks.This thermo-chemicaland the consequent thermo-mechanical stressesdestruct the texture of the bricks, even thehigh quality spinel bricks
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bricks bricks adjacent totipcasting under gone severe thermal stresses The horizontalCracks are quite visible
Stresses on spinel bricks
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Pinch at retainer rings
Phenomena
collapse of brick ringsagainst retainer rings andoutlet segments from pinch spalling
Symptoms
Horizontal cuts and crackof bricks at the upper edge
of retainer and transposing nose ring
segments
Reasons
• Thrust and oscillations generate shear cracks and
grinding • Flexing kin or ovality
accelerate the damage
Improvements
Stiff kiln shellno nose shaped bricksUse double retainer rings or conical retainer rings..
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Stresses on the bricks at and on the retainer ring
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Crushing of bricks near the ring area
Shear cracks on the bricks adjacent to retainer ringdue to excessive axial thrust
Retainer ring
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Bricks crushed, twisted and sheared at the retainer ringby excessive axial thrust
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Even the tip casting blocks got uprooted due to excessive thrust. Tip of the shell is totally damaged.
Excessive thrust on the tip
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The old type retainer ring is unable to arrest the thrust.
thrust
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Excessive thrust at the junction of the cone and cylinder in a FLS kiln(APCW). Even the cone fails to reduce the thrust. The bricks are Spinel bricks.
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Excessive thrust shear the bricks even the top -grade spinel grade. The bricks before the retainer ring got lifted.Application of adequate mortar is a must forbrick lining at the nose ring area.
APCW)
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Bricks got uprootedat retainer ring(APCW)
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Bottom half of theBricks are missing. They got ground due
to excessive friction Bricks must have
full contact withretainer ring
Mortar is a must to overcome ovality and bell mouth.
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Retainer ringsThe reasons for creating hotspots are as follows :
1. All magnesia – containing bricks tend , because of theirexpansion ranging from 1.6 to 1.8 % ,to expand in the
direction of kiln inlet when the kiln is actually heated up.In these conditions the brick rings situated beneath theretainer ring are already pushed into or in some cases over the retainer ring and are thus damaged.
2. If some coating is slowly built up in the sintering zone , the temperature of the brickwork decreases leading to re expansion during which the retainer rings have tocompensate the forces from the brickwork of the whole sintering zone
3. Bricks must have full contact with retainer ring .Other wisethe bricks undergo severe stresses and get crushed.
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Here the v –joint created is due to either the blocks are over heatedand so the collar got distorted or; the collar does not have smooth surfaceand so the brick does not have full face contact which makes the brickslant.Another strong reason is shell tip has bell mouth. The brickring before the retainer ring got lifted from the shell by 30 to 40 mm
At the retainer ring the bricks are crushed as most of the bricks did not have full face contact with retainer ring because of welding seams. This has to be ground to smooth surface..
In many areas retainer ring was exposed
1200 mm
Nose ring area at AC
Almag -85 Almag AF
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HA-70 bricks twisted at 47 m
Castings got oxidised
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.
Bricks adjacentto retainer ringgot crushed
AC
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Welding joints
This welding joint will not allow the brick to havefull face contact and the brick undergoes stresses under dynamic conditions ,gets twisted and crumbled. This needsgrinding to smooth surface to have 100% contact.Almag AF ishighest class spinel brick which too failed in this area.
This point has highlyconcentrated stress.Retainer ring
thrust Crack propagation
AC
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Retainer ring
thrust
After grinding the brick has full contact with the retainer ring.
Kiln shell
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1200 mm
Recommended lining for tip castingand at retainer ring ( AC)
High grade spinel brick
300 mm L Almag –85 orAlmag AF
High grade spinel brick with 300mm L is also recommended to achieve better life.Normal spinel brick CCS(cold crushing strength) = 400 Kgs / sq cmhigh grade spinel brick = 700 Kgs/ sq cm
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Modification of retainer ring Increase the hollow space to have more welded surface
Here the welding joint can be avoided orthe welding can beground tosmooth surface
Hollowspace to weldretainer ringto the kiln shelland filled withcastable
Retainer ring should have a full contact with the brick
In correct
correct
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Nose ring block, designed by PSBfor spinel brick lining
Please note that the bricks have full contact with faceOf the casting.
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PSB ‘S design
Please note that the bricks have full contact with faceOf the casting.
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SIFCA
It is an excellantCompromise betweenmetallic alloyand refractoriesIt is as tough asmetal and as wearand heat resistant asrefractories.
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This kind of cowl shell of PSB design will provideeffective cooling
PSB ‘S design
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RHI design – Tip casting
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The surfaceis coated byTungstencarbide
Tip casting designed by Brok-Hausen
Castable
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FLS designOut let sectors
The nose is lined withlow cement castablewhich protects thecastings from heatand clinker dustabrasion
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Here the castings get oxidiseddue to high secondary air temperatureAnd hence it needs extra cooling.
Refratecknik design
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Retainer ring -Refratechnik
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RHI lining with FLS tip casting
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RHI design – Tip casting
Abrasion Resistant castable
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Nose ring – Harbison walker
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Refratecknik ‘s lining recommendation for a FLS kiln
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Conical retainer rings to reduce the thrust on thebricks designed by Magattoux and RHI
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Conical retainer rings to reduce the thrust on thebricks designed by Magattoux and RHI
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Conical retainer ring
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Double retainer ring
Some plants use two retainer rings but it has not reducedaxial thrust.
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1.6 m
10 mm ceramic blanketon the cone which is notCorrect . It should be on thecylinder
This is a high stress zone as there is point contact
The lining at the junction of the cone and cylinderFLS kilns(GCW)
198 mm
2 mm expansion joint
198 mm
Please note that the diamond bricks should never crossthe cone either way as it creates a v-joint
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30 mm
Recommended for better thrust relief
168 mm198 mm 198 mm
For this the end brick needs cuttingie., reduction in L from 198 to 168 mm.To avoid cutting of bricks theretainer ring can also be shifted by 30 mm. The exp.joint is on the cylinder.
There should be face contact not point contact
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1.0 m 0.97 m
30 mmCeramic board
Recommended expansion joint
5 mm ceramic board
300 mm 300mm 198mm 172
Ceramic board placed on the retainer ring
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400 mm
1200
mm
267 mm
933 mm
Anchors arestaggered. As per the chart the spacingis 217 mm. As the width is only 400 mm it is not possible to fix the anchors with 217 mmspacing . We can have170mm or 160 mmspacing and see the anchor headdoes not cross the otheranchor nor of the other block. Anchorsare to be coated bybitumen or wax
170 mm
170 mm
5mmCeramic boardas expansion joint.
Anchor spacing for casting at nose ring area
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Maximum anchor spacingAnchor diamter (mm)
Lining thickness (mm)
6 φ 8 φ 10 φ 13 φ
75
100
125
150
200
250
300
354 472 590 767
306 409 511 664
274 365 457 594
250 334 417 542
217 289 361 470
194 258 323 420
177 236 295 383
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Straight expansionjoints
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Nose ring casting
Note the expansion joint is straightand distinct. No over lapping
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Castable at nose ring
Please notethat expansion joints are distinct andstraight
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Nose ring casting by Hasle
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Pre cast nose ring blocks
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Clear expansion joints expansion must be be distinctly visible aftercasting at nose ring area
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Pre cast blocks fixed on retainer rings
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Lining at retainerring area
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