Reffailue nosering pradeep kumar

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



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.



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



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



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



Nose ring cooling air = 70 m / sWell directed to cool the blocks

5mm ceramic fiber board

Latest tip casting



Nose ring cooling air is directed on kiln shellthe air is preheated and will not cool the castings- incorrect practice



Wear on refractory due to incorrect 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.



Lack of expansioncauses spalling

GCW



Inadequate expansion between two monolithic blockscauses this spalling GCW



Crack formationafter one monthoperation.This is due to inadequateexpansion

APCW



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



In sufficient expansionjoint at the junction oftwo blocks. Minimum5 mm expansion joint

Is necessary

APCW



Expansion not givenproperly

Spalling has startedafter one month’s operation

APCW



Dense surfacedue to more compaction due to

excessive vibration which does notallow the steam escape.

(ACW)



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

(ACW)



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



Mechanical stresses on the refractories



Shear cracks due to excessive thrust on bricks adjacent to tip casting



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



bricks bricks adjacent totipcasting under gone severe thermal stresses The horizontalCracks are quite visible

Stresses on spinel bricks



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..



Stresses on the bricks at and on the retainer ring



Crushing of bricks near the ring area

Shear cracks on the bricks adjacent to retainer ringdue to excessive axial thrust

Retainer ring



Bricks crushed, twisted and sheared at the retainer ringby excessive axial thrust



Even the tip casting blocks got uprooted due to excessive thrust. Tip of the shell is totally damaged.

Excessive thrust on the tip



The old type retainer ring is unable to arrest the thrust.

thrust



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.



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)



Bricks got uprootedat retainer ring(APCW)



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.



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.



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



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



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



Retainer ring

thrust

After grinding the brick has full contact with the retainer ring.

Kiln shell



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



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



Nose ring block, designed by PSBfor spinel brick lining

Please note that the bricks have full contact with faceOf the casting.



PSB ‘S design

Please note that the bricks have full contact with faceOf the casting.



SIFCA

It is an excellantCompromise betweenmetallic alloyand refractoriesIt is as tough asmetal and as wearand heat resistant asrefractories.



This kind of cowl shell of PSB design will provideeffective cooling

PSB ‘S design



RHI design – Tip casting



The surfaceis coated byTungstencarbide

Tip casting designed by Brok-Hausen

Castable



FLS designOut let sectors

The nose is lined withlow cement castablewhich protects thecastings from heatand clinker dustabrasion



Here the castings get oxidiseddue to high secondary air temperatureAnd hence it needs extra cooling.

Refratecknik design



Retainer ring -Refratechnik



RHI lining with FLS tip casting



RHI design – Tip casting

Abrasion Resistant castable



Nose ring – Harbison walker



Refratecknik ‘s lining recommendation for a FLS kiln



Conical retainer rings to reduce the thrust on thebricks designed by Magattoux and RHI



Conical retainer rings to reduce the thrust on thebricks designed by Magattoux and RHI



Conical retainer ring



Double retainer ring

Some plants use two retainer rings but it has not reducedaxial thrust.



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



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



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



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



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



Straight expansionjoints



Nose ring casting

Note the expansion joint is straightand distinct. No over lapping



Castable at nose ring

Please notethat expansion joints are distinct andstraight



Nose ring casting by Hasle



Pre cast nose ring blocks



Clear expansion joints expansion must be be distinctly visible aftercasting at nose ring area



Pre cast blocks fixed on retainer rings



Lining at retainerring area



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Reffailue nosering pradeep kumar