Refractory Failure at Nose Ring

Refractory failure at nose ring and cooling zone of kiln

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Causes for refractory failure uncontrollable axial thrust due uneven expansion etc

In adequate space for expansion

Wear on refractory due to in- correct selection and wrong installation

Shell warpage or ovality bell mouth formation ( mechanical stresses)

Burning of castings

Thermo-chemical stresses and thermo mechanical stresses In- correct design of retainer rings or wrong location

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Failure of castables

Axial thrust and inadequate expansion Axial thrust is always there on the nose ring refractories . This is due to the inclination of kiln and the expansion of bricks. If refractories cannot withstand they crumble.Though FLS kilns have outlet cone to arrest the thrust in some of the kilns the thrust is still on the nos ering area. 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. 10 to 30 mm ceramic pads

2 mm SS shim on retainer ring To be filled with castable.

4 mm ceramic board on the casting 2 mm expansion card board this is applicable to brick lining too For alumina bricks no expansion when it is used on tip casting PDF created with pdfFactory Pro trial version www.pdffactory.com

Less tip casting casting life 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.. 5 mm ceramic board on the retainer ring

4mm ceramic board

2 mm expansion cardboard joints

2 mm Ceramic boards

castable

Very important is nose ring velocity per nozzle is > 60 m/ s and 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. PDF created with pdfFactory Pro trial version www.pdffactory.com

to arrest the axial thrust due to extra expansion with ceramic fiber boards can be given. 4mm ceramic fiber boards 5 mm ceramic board ( which can withstand on the retainer ring 1200 deg c) on the casting

2 mm card board

Anchors are of SS310 steal grade with correct spacing PDF created with pdfFactory Pro trial version www.pdffactory.com

Axial thrust

178 198 198

The brick which is under maximum thrust and stress Tip shall be always curve shaped 198 198mm

1000 mm 230 230

230

300L

If we increase the length it may withstand some more thrust.

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Latest tip casting 5mm ceramic fiber board

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

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Nose ring cooling air is directed on kiln shell the 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 Andalusite based castables are suitable.Corundum based castables are good wear resistant but they are easily attacked by free lime and excessive liquid.They are very sensitive to steam formation. Magnesia spinel bricks can take more thermoMechanical 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 expansion causes spalling GCW PDF created with pdfFactory Pro trial version www.pdffactory.com

Inadequate expansion between two monolithic blocks causes this spalling GCW PDF created with pdfFactory Pro trial version www.pdffactory.com

APCW

Crack formation after one month operation.This is due to inadequate expansion

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APCW

Castable dislodged from the shell due to wrong installation .Inadequate expansion joints caused spalling.The life is only 3 months

Initial cracks after 1 month of operation PDF created with pdfFactory Pro trial version www.pdffactory.com

APCW

In sufficient expansion joint at the junction of two blocks. Minimum 5 mm expansion joint Is necessary

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APCW

Expansion not given properly

Spalling has started after one month’s operation

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Dense surface due to more compaction due to excessive vibration which does not allow the steam escape. (ACW)

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Castable bursts due to un controlled steam pressure , 11 hr after initial heat-up (ACW)

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Steam explosion 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.

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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-chemical and the consequent thermo-mechanical stresses destruct the texture of the bricks, even the high quality spinel bricks PDF created with pdfFactory Pro trial version www.pdffactory.com

Stresses on spinel bricks

bricks bricks adjacent to tipcasting under gone severe thermal stresses The horizontal Cracks are quite visible PDF created with pdfFactory Pro trial version www.pdffactory.com

Phenomena

Symptoms

collapse of brick rings against retainer rings and outlet segments from pinch spalling

Horizontal cuts and crack of bricks at the upper edge of retainer and transposing nose ring segments

Pinch at retainer rings Reasons • Thrust and oscillations generate shear cracks and grinding • Flexing kin or ovality accelerate the damage PDF created with pdfFactory Pro trial version www.pdffactory.com

Improvements Stiff kiln shell no nose shaped bricks Use double retainer rings or conical retainer rings..

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 ring due to excessive axial thrust

Retainer ring

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

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

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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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APCW) 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 for brick lining at the nose ring area. PDF created with pdfFactory Pro trial version www.pdffactory.com

Bricks got uprooted at retainer ring (APCW) PDF created with pdfFactory Pro trial version www.pdffactory.com

Bottom half of the Bricks are missing. They got ground due to excessive friction Bricks must have full contact with retainer ring Mortar is a must to overcome ovality and bell mouth.

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Retainer rings The reasons for creating hotspots are as follows : 1. All magnesia – containing bricks tend , because of their expansion 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 the retainer 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 to compensate the forces from the brickwork of the whole sintering zone 3. Bricks must have full contact with retainer ring .Other wise the bricks undergo severe stresses and get crushed. PDF created with pdfFactory Pro trial version www.pdffactory.com

Nose ring area at AC

Almag -85

1200 mm

Almag AF

Here the v –joint created is due to either the blocks are over heated and so the collar got distorted or; the collar does not have smooth surface and so the brick does not have full face contact which makes the brick slant.Another strong reason is shell tip has bell mouth. The brick ring before the retainer ring got lifted from the shell by 30 to 40 mm In many areas retainer ring was exposed

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.. PDF created with pdfFactory Pro trial version www.pdffactory.com

AC HA-70 bricks twisted at 47 m Bricks adjacent to retainer ring got crushed V-joint gap due to bell mouth Or casting got sunk. If casting face is not smooth it can create this gap. This need a machined Surface. Point contact is not acceptable.

Castings got oxidised

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AC thrust

Crack propagation

Welding joints This point has highly Retainer ring concentrated stress. This welding joint will not allow the brick to have full face contact and the brick undergoes stresses under dynamic conditions ,gets twisted and crumbled. This needs grinding to smooth surface to have 100% contact.Almag AF is highest class spinel brick which too failed in this area. PDF created with pdfFactory Pro trial version www.pdffactory.com

thrust

Kiln shell

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

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Recommended lining for tip casting and at retainer ring ( AC) High grade spinel brick

1200 mm 300 mm L Almag –85 or Almag 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 cm high grade spinel brick = 700 Kgs/ sq cm

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Modification of retainer ring In correct

Hollow space to weld retainer ring to the kiln shell and filled with castable

Increase the hollow space to have more welded surface correct

Here the welding joint can be avoided or the welding can be ground to smooth surface

Retainer ring should have a full contact with the brick PDF created with pdfFactory Pro trial version www.pdffactory.com

Nose ring block, designed by PSB for spinel brick lining Please note that the bricks have full contact with face Of the casting.

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PSB ‘S design

Please note that the bricks have full contact with face Of the casting.

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SIFCA

It is an excellant Compromise between metallic alloy and refractories It is as tough as metal and as wear and heat resistant as refractories.

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PSB ‘S design

This kind of cowl shell of PSB design will provide effective cooling

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RHI design – Tip casting

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Tip casting designed by Brok-Hausen

The surface is coated by Tungsten carbide

Castable

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FLS design Out let sectors

The nose is lined with low cement castable which protects the castings from heat and clinker dust abrasion

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Refratecknik design

Here the castings get oxidised due to high secondary air temperature And hence it needs extra cooling. PDF created with pdfFactory Pro trial version www.pdffactory.com

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 the bricks designed by Magattoux and RHI

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Conical retainer rings to reduce the thrust on the bricks 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 reduced axial thrust.

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The lining at the junction of the cone and cylinder FLS kilns(GCW) 10 mm ceramic blanket on the cone which is not Correct . It should be on the cylinder This is a high stress zone as there is point contact

2 mm expansion joint 198 mm

198 mm

1.6 m

Please note that the diamond bricks should never cross the cone either way as it creates a v-joint PDF created with pdfFactory Pro trial version www.pdffactory.com

Recommended for better thrust relief

30 mm

168 mm 198 mm 198 mm

For this the end brick needs cutting ie., reduction in L from 198 to 168 mm. To avoid cutting of bricks the retainer ring can also be shifted by 30 mm. The exp.joint is on the cylinder.

There should be face contact not point contact PDF created with pdfFactory Pro trial version www.pdffactory.com

Recommended expansion joint

Ceramic board placed on the retainer ring

5 mm ceramic board

30 mm Ceramic board

300 mm 300mm 198mm 172

1.0 m PDF created with pdfFactory Pro trial version www.pdffactory.com

0.97 m

Anchor spacing for casting at nose ring area 400 mm

1200 mm

170 mm

5mmCeramic board as expansion joint.

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Anchors are staggered. As per 267 mm the chart the spacing is 217 mm. As the width is only 400 mm it is not possible to fix the anchors with 217 mm spacing . We can have 170mm or 160 mm 933 mm spacing and see the anchor head does not cross the other anchor nor of the other block. Anchors are to be coated by bitumen or wax

170 mm

Maximum anchor spacing Anchor diamter (mm)

6φ

8φ

10 φ

13 φ

Lining thickness (mm) 75 100 125 150 200 250 300

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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 expansion joints

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Nose ring casting Note the expansion joint is straight and distinct. No over lapping

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Castable at nose ring

Please note that expansion joints are distinct and straight

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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 after casting at nose ring area PDF created with pdfFactory Pro trial version www.pdffactory.com

Pre cast blocks fixed on retainer rings

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Lining at retainer ring area PDF created with pdfFactory Pro trial version www.pdffactory.com