Refractory Failure at Nose Ring

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Refractory failure at

nose ring and cooling zoneof kiln

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uncontrollable

axial thrust dueuneven expansion

etc

Shell warpage

or ovality

bell mouth

formation

( mechanical

stresses)

Wear on refractory due to

incorrect selection andwrong installation

In- correct design

of retainer rings or

wrong location

In adequate

space for expansion

Causes for refractory failure

Thermo-chemical

stresses and thermo

mechanical stresses Burning of

castings

Failure of

castables






Axial thrust and inadequate expansion Axial 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 ringbase 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 casting

this is applicable to brick lining too

when it is used on tip casting

2 mm SS shim on retainer ring10 to 30 mm

ceramic pads

2 mm expansion card board

For 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 andclinker dust entrainment. If we give castable lining on the hot faceside of castings we can increase the life of the castings. Most of theplants face this problems with brick lining on nose ring..

castable2 mm expansioncardboard joints

4mm ceramic board5 mm ceramic board

on the retainer

ring

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.

Less tip casting casting life

2 mm Ceramic

boards






to arrest the axial thrust due to extra expansion with ceramic

fiber 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 thrust

and stress

300L230230230

If we increase the length it may

withstand some more thrust.

Tip shall be always

curve 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 shell

the 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 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 thermo-

Mechanical and thermo-chemical stresses at the

nose ring area. Proper expansion is a must to reduce spallingdue to expansion. The function of ceramic board is to

accommodate the thrust coming from expansion.






Lack of expansion

causes spalling

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Inadequate expansion

between two monolithic blocks

causes this spalling GCWPDF created with pdfFactory Pro trial version www.pdffactory.com





Crack formation

after one monthoperation.This is

due to inadequate

expansion

APCW






Castable dislodged from the shell

due to wrong installation .Inadequate

expansion joints caused spalling.Thelife is only 3 months

Initial cracks

after 1 month

of operation

APCW






In sufficient expansion

joint at the junction of two blocks. Minimum

5 mm expansion joint

Is necessary

APCW






Expansion not given

properly

Spalling has startedafter one month’s operation

APCW






Dense surface

due to more compaction due to

excessive vibration which does not

allow the steam escape.(ACW)






Castable bursts due to

un controlled steam pressure ,

11 hr after initial heat-up

(ACW)






Castable bursts due touncontrolled 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 whichburns 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 stresseson the refractories






Shear cracks due to excessive

thrust on bricks adjacent to tip casting






Liquid infiltration into the brickand damage the bricks.This thermo-chemical

and the consequent thermo-mechanical stresses

destruct the texture of the bricks, even the

high quality spinel bricks






bricks bricks adjacent to

tipcasting under gone severe

thermal stresses The horizontal

Cracks are quite visible

Stresses on spinel bricks






Pinch at

retainer rings

Phenomena

collapse of brick rings

against retainer rings andoutlet segments from

pinch spalling

Symptoms

Horizontal cuts and crack

of bricks at the upper edgeof retainer and

transposing nose ring

segments

Reasons

• Thrust and oscillationsgenerate shear cracks and

grinding

• Flexing kin or ovality

accelerate the damage

Improvements

Stiff kiln shellno nose shaped bricks

Use 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 ring

due to excessive axial thrust

Retainer ring






Bricks crushed, twisted and sheared at the retainer ring

by excessive axial thrust






Even the tip casting blocks got uprooteddue 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 brickseven 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.

APCW)






Bricks got uprooted

at retainer ring

(APCW)






Bottom half of the

Bricks are missing.They got ground due

to excessive friction

Bricks must have

full contact with

retainer ringMortar is a must to

overcome ovality

and bell mouth.






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 tocompensate 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.






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 brickslant.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

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 mouth

Or casting got sunk. If casting

face is not smooth it can create

this gap. This need a machinedSurface. Point contact is not

acceptable.

Bricks adjacentto retainer ring

got crushed

AC






Welding joints

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.

This point has highly

concentrated 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 casting

and at retainer ring ( AC)

High grade spinel brick

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






Modification of retainer ringIncrease the

hollow space to have

more welded surface

Here the welding joint

can be avoided or

the welding can beground to

smooth surface

Hollow

space to weld

retainer ring

to the kiln shelland filled with

castable

Retainer ring should have a full contact with the brick

In correct

correct






Nose ring bloc k, designed by PSB

for sp inel br ick l in ing

Please note that the bricks

have full contact with face

Of the casting.






PSB ‘S design

Please note that the bricks

have full contact with face

Of the casting.






SIFCA

It is an excellant

Compromise between

metallic alloy

and refractoriesIt is as tough as

metal and as wear

and heat resistant as

refractories.






This kind of cowl shell of PSB design will provide

effective cooling

PSB ‘S design






RHI design – Tip casting






The surface

is coated by

Tungsten

carbide

Tip casting designed by Brok-Hausen

Castable






FLS design

Out let sectors

The nose is lined withlow cement castable

which protects the

castings from heat

and clinker dust

abrasion






Here the castings get oxidised

due to high secondary air temperature

And hence it needs extra cooling.

Refratecknik design






Retainer ring -Refratechnik






RHI lining with FLS tip casting








Nose ring – Harbison walker






Refratecknik ‘s lining recommendation for a FLS kiln






Conical retainer rings to reduce the thrust on the

bricks designed by Magattoux and RHI






Conical retainer rings to reduce the thrust on the

bricks designed by Magattoux and RHI






Conical retainer ring






Double retainer ring

Some plants use two retainer rings but it has not reduced

axial thrust.






1. 6 m

10 mm ceramic blanket

on the cone which is not

Correct . It should be on th

cylinder

This is a high stress zone as there is

point contact

The lining at the junction of the cone and cylinder

FLS kilns(GCW)

198 mm

2 mm expansion joint

198 mm

Please note that the diamond bricks should never cross

the cone either way as it creates a v-joint






30 mm

Recommended for better thrust relief

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 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 m0.97 m

30 mm

Ceramic boar

Recommended expansion joint

5 mm ceramic board

300 mm 300mm 198mm 172

Ceramic board placed on the retainer ring






400 mm

1 2 0 0 m m

267 mm

933 mm

Anchors are

staggered. As per

the chart the spacing

is 217 mm. As the width

is only 400 mm

it is not possible to fix

the anchors with 217 mmspacing . We can have

170mm or 160 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

170 mm

5mmCeramic board

as expansion joint.

Anchor spacing for casting at nose ring area






Maximum anchor spacing

Anchor 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 expansion joints






Nose ring casting

Note the expansion joint is straight

and distinct. No over lapping






Castable at nose ring

Please note

that expansion joints are distinct and

straight






Nose ring casting by Hasle






Pre cast nose ring

blocks






Clear expansion joints expansion

must be be distinctly visible after

casting at nose ring area






Pre cast blocksfixed on retainer rings






Refractory Failure at Nose Ring

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