refractory failure at nose ring
TRANSCRIPT
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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
in- correct 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
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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.
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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
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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
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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
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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 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 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.
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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
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Crack formation
after one monthoperation.This is
due to inadequate
expansion
APCW
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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
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In sufficient expansion
joint at the junction of two blocks. Minimum
5 mm expansion joint
Is necessary
APCW
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Expansion not given
properly
Spalling has startedafter one month’s operation
APCW
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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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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
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Mechanical stresseson 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 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
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bricks bricks adjacent to
tipcasting under gone severe
thermal stresses The horizontal
Cracks are quite visible
Stresses on spinel bricks
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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..
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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 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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Even the tip casting blocks got uprooteddue 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 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)
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Bricks got uprooted
at retainer ring
(APCW)
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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.
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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 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.
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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
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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
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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
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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 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
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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
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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.
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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 refractoriesIt is as tough as
metal and as wear
and heat resistant as
refractories.
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This kind of cowl shell of PSB design will provide
effective cooling
PSB ‘S design
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RHI design – Tip casting
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The surface
is coated by
Tungsten
carbide
Tip casting designed by Brok-Hausen
Castable
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FLS design
Out let sectors
The nose is lined withlow cement castable
which protects the
castings from heat
and clinker dust
abrasion
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Here the castings get oxidised
due to high secondary air temperature
And 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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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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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
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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
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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
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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
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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
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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
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Pre cast blocksfixed on retainer rings
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