RING AND SNOW BALL FORMATIONIN THE KILN

Sinter Ring at the junction of burning zone and transition zone

Spurrite and

Sulfo-spurrite ring

In calcining zone

Reduction in kilnDiameter due toRing formation

Raw mix ChemistryVariation in chemistry

Flame &temperatureCombustion

Un stable kiln andcalciner operation

Key reasons for ring formation

Combustion

Selection ofrefractories

Hard BurningDue to the presence ofCalcite and Quartzite Volatile

recycling

All reasons are inter-dependent and flame

and combustion plays a very major role

Fuel characteristics

The formation of a ring is a dynamic process in which the

factors responsible for formation outweigh the forces of

destruction.

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:

SINTER RING

• 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:

• Process.

• Operation.

• Maintenance.

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

Calcium LangebeiniteK2Ca2(SO4)3

>1250 ______

Porosity of the brick may help to reduce ring formation but atthe cost of heat loss. It can be reduced but it cannot be avoided.

Closed pores

Porosity of the kiln brick

Open pores

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.

Uniform coating 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 is calcination 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 inthe 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

cleaner kilns.

Spurrite Rings:Carbonate or spurrite rings are formed through CO2desorption intothe 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

composition C2S.CaCO3.

Spurrite is a form of carbonated belite. When the carbonate in Spurrite 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.

Alkali rings: 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 of recovery kilns, for example, where alkali is always in excess of

sulfur, severe ringing and balling sometimes occur.

-Statement by an experienced process man

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

around

1200 deg c

Spurrite ring in kiln calcining zone

Sulfo Spurrite -SEM

Chemical Analysis of spurrite ring layer by layer

-- study by RHI,Vienna

Sulfo Spurrite ring -SEM

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

Favorable temperature profile

Influence of flame length on volatile recycle and thermal stability

1500

degc

1200

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

Unfavorable Temperatureprofile, flat

Favorable area for spurrite ring

formation

1000

1500

1200

1000

(- Reference from PCA)

Reference from Blue circle literature

( Holcim)

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

Stoppages.

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 thanmagnesite Bricks.

Shark teeth

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 .

Shark teeth

By simple to and fro movement of swirler tip and by alteration of primary airPressure at burner inlet , can change length and shape of the flame.Novaflam is user friendly ,simple and very versatile burner.

DdD

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 amagician 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

Baroda