RING AND SNOW BALL FORMATION
IN THE KILN
Sinter Ring at the junction of burning zone and transition zone
In calcining zone
Reduction in kiln
Diameter due to
Raw mix Chemistry
Variation in chemistry
Un stable kiln and
Key reasons for ring formation
Due to the presence of
Calcite and Quartzite Volatile
All reasons are inter-dependent and flame
and combustion plays a very major role
The formation of a ring is a dynamic process in which the
factors responsible for formation outweigh the forces of
The forces considered to cause deposit formation can be
grouped as follows:
• Melting or freezing due to addition or removal of heat.
• Interlocking of aggregates built up of finer particles hold
together by surface forces.
• Interlocking of long fibrous particles.
In general, chemical composition of the sinter ring material is that of
the clinker with no appreciable concentration of volatile elements.
From a mineralogical viewpoint, the normal clinker minerals like alite,
belite and free CaO are observed. The bonding mechanism
responsible for sinter ring formation is the freezing of the clinker.
The rings, depending on their origin, may be dense or porous, and
may develop slowly or just in a few hours. The first symptoms of
ring formation are:
• A higher negative pressure before the exhaust fan.
• Incomplete fuel combustion as indicated by "CO" analyzer.
• Intermittent charge retention.
• Abnormal temperature gradients in the kiln shell.
• Higher amperages in the kiln motor.
The reasons for ring formation, well agreed between many plant
operators, may be classified in three groups:
The next group deals with operation troubles that can lead to
ring formation. These are:
• Discontinuous feed.
• Material segregation.
• Flame pattern and position.
• Improper combustion.
• Successive kiln upsets.
Material segregation is not an uncommon situation in
rotary kiln. For instance, the lime content we have in the
meal, loss on ignition free, never coincides with the lime
content in the clinker. The lighter lime particles are easily
carried by the gases, while silica, iron oxide and alumina
particles follow down the kiln into the burning zone.particles follow down the kiln into the burning zone.
Depending on the degree of segregation, excess liquid may
form in the burning zone, and even outside, if the melting
point of the glass is lowered by segregation. The addition of
sand in the raw materials modifies significantly the burnability
because it shows lower reactivity and grindability. The
grinding of quartz, during assemblage grinding, causes quartz
concentration in the coarse fractions of raw mix and
consequently material segregation in the kiln charge.
In the maintenance group we find:
• Defective burner.
• Defective instrumentation.• Defective instrumentation.
• False air admission
Porosity of the brick may help to reduce ring formation but at
the cost of heat loss. It can be reduced but it cannot be avoided.
Porosity of the kiln brick
Silica infiltrated surface or vitrified surface on brick can avoid infiltration of low melting ,low
Viscous components .This avoids destruction of refracories but spurrite rings cannot
be avoided fully. Properly balanced chemistry , well tuned flame with hot and oxdised
conditions and properly operated kiln and Calciner can only elimiinate ring formation or
reduce the aggravation.
Preferably 5 or 6 %
Of the diameterStrong intense flame plays a major role
In kiln coatng stablity
What is the different between sulphur, spurrite, and alkali rings
and how can we distinguish between these three?
Formation of type of ring is based upon the kiln system
atmosphere.If sulfur is excess in raw material and fuel then
sulphate ring is formed due to formation of spurrite and
sulphospurrite mineral.Sulphate ring generally formed in
calcination zone and it is very hard in nature.Alkali ring iscalcination zone and it is very hard in nature.Alkali ring is
formed when alkali is present in excess than the sulphur in
raw material and fuel.When high alkali concentration in raw
material then Arcanite(K2SO4),Aphthitalite[K3Na(SO4)2] , and
Thenardite[Na2SO4] mineral formed.You may analyse the
coating sample by XRD to know the cause of coating
formation and type of ring.
Sulphur Rings: Sulphur-induced rings are formed when the
molar sulfur to alkali ratio in
the system is more than 1.2. In such cases, there is a
considerable amount of free SO3 circulating in the kiln. At a
certain concentration level in the kiln gas, sulfation of the free
lime occurs with anhydrite formation (CaSO4). If the kiln is
burning under slightly reducing conditions, more volatile and
lower melting sulfur salts may form, therefore increasing the
severity of the problem. The salts, in molten state, coat the
traveling clinker dust, forcing it to stick to the kiln wall in the form
of rings. Sometimes the chemical analysis of such rings does
not indicate high sulfur concentrations, proving that even a small
amount of free sulfur is sufficient to cause rings. The severity of
the problem increases with the dust concentration in the kiln
gas. Dustier kilns have a tendency to form more rings than
Carbonate or spurrite rings are formed through
the freshly formed free lime, or even through belite
recarbonation. These rings are hard, layered, and exhibit the
same chemistry as regular clinker. X-ray diffraction however,
clearly indicates the presence of spurrite, a mineral with
Spurrite is a form of carbonated belite. When the carbonate inSpurrite is a form of carbonated belite. When the carbonate in
the spurrite is replaced with sulfur the new mineral is called
sulfated spurrite. Spurrite rings form whenever the partial
pressure of CO2 above the bed of material is high enough to
invert the calcining
reaction. In coarsely ground, silica-rich raw mixes, the free lime
does not have sufficient time in the calcining zone to react with
silica, therefore increasing the chances for spurrite deposits.
The third type of ring occurs whenever the sulfur-to-alkali
molal ratio is( encrustration index)
less than 0.83, usually in kilns with heavy chlorine loads. In such
cases, low-melting potassium salts provide the binder for clinker
dust travelling up the kiln. Through a "freeze-and-thaw"
mechanism, these rings can assume massive proportions. Alkali
rings are far less common than other types because sulfur and
carbonates usually are in excess relative to potassium. In lime
recovery kilns, for example, where alkali is always in excess ofrecovery kilns, for example, where alkali is always in excess of
sulfur, severe ringing and balling sometimes occur.
Long and lazy flame reduce the calcining zone length and increase the temperature. It increases
Volatility of sulfur and alkalies ,increase the recirculation, and increase the low melting sufites .The
rawmeal soaked in this temperature, in this low melting alkali and calcium sufites. gets balled up .As
it reaches the burning zone it steals some more liquid , increases its size and many times blocks the
flame causing deflection and impinges causing damage the refractory.
Snow ball formation
This is the result of bad flame which I witnessed In my own plant in my short
tenure. 72 hours stoppage , loss of 11000 tons of clinker or 11 million Indian
rupees as net cash loss. More over it is an unsafe activity
Do you need such condition and stoppage of kiln ?.
Snow ball formation as a result of ring formation and bad flame.
Low gas retention time in calciner further aggravate the situation
which we directly witnessed it. ILC is less friendly than SLC as far
as gas retention and combustion efficiency is concerned but NOX
emission is higher in SLC than that of in ILC where
denoxification is achieved.
Bad flame activate the volatile
recirculation esp sulfur and alkalies
Short and intense flame ,low back end temperature ,low volatile recycle
More absorption of sulfur and formation of more
thermally stable sulfates of alkali and calcium
Influence of flame length on volatile recycle and thermal stability
Long flame ,high back end temperature ,high volatile recycle
Less sulfur volatile absorption and formation of more
thermally unstable stable sulfites of alkali and calcium
Favorable area for spurrite ring
Reference from Blue circle literature
Fives Pillard’s novaflam got the ability to slice the ring and
avoid 3 days Stoppage.
The burner can be more inclined ,shape the flame closer to the ring which reduces the
Thickness. The jack and knuckle ball arrangement in the telescopic piece allow this
up and down motion Which only Nova flam has.
Pillard ‘s Novaflam got the ability to slice the ring and avoid 3 days
The burner can be more inclined ,shaped the flame closer to the ring which reduces the
Thickness. The jack and knuckle ball arrangement in the telescopic piece allow this
up and down motion Which only Nova flam has..Caution –extra care must be taken
When High alumina bricks are used which is inferior in its thermal properties than
Shark teeth forms when ash in coal is high and high dust circulation from cooler to kiln.
This makes the clinker more sticky and many occasions lead to snow man formation on
Static cooler and rhino horn on burner. Chemistry ,if it is not controlled can lead to dusty
Clinker and shark teeth at the kiln tip.By pushing the burner in and adjusting flame gives
great relief to this problem.Cooler air distribution also reduces this problem.
Shark teeth lead segregation in the clinker discharge and leads to red river in the cooler .
By simple to and fro movement of swirler tip and by alteration of primary air
Pressure at burner inlet , can change length and shape of the flame.
Novaflam is user friendly ,simple and very versatile burner.
Do you need a old time master burner who does jugglery now and then to tune the flame
by adjusting two or three valves for axial,radial and stabilising air like a
magician on the Stage. Nova flam says “NO”. Novaflam has simple operation unlike
complicated operation with other burners. More user friendly than any other burner.
Make the kiln smile with good flame
or you will weep
Novaflam makes you to smile
Thank you for your kind attention
PRADEEP KUMARPRADEEP KUMAR
Technical advisor - commissioning
Fives combustion pvt ltd