Dusty clinkerMore melt due to alkali or sulfur recycleDistorted flameDisintegration of clinker due to reduced conditionsBlow back of dust from cooler to kiln and recyclingHigh air flow rate in first portion of clinker (, incorrect air distribution)Causes
Dusty clinker formationWhen the kiln is dusty the snow man problem starts. The dust falls on the coolerand blows back into the kiln which is carried away by secondary air stream. Ifsecondary velocity is more than 5 m/s the finer dust is carried into the kiln and thevelocity of combustion air and combustion products further shoots up near the flamewhich carries the dust further in side the burning Zone. This dust steals some liquid fromthe burning zone and falls on the cooler and the cycle continues between cooler to kiln.It reaches a stage the clinker dust becomes so sticky that it sticks to the side andvertical wall of the cooler and dust build –up called snow man forms. If horse shoeis there in the front side of the it has favorable base to form. If sulfur and alkalirecycle is there inside the kiln the melt increases , which does not reflect inthe calculated liquid , the minor low melting compounds concentrate more on dustyfraction of the clinker.Though we donot have much control on minerlogy some critical parameters canbe controlled by operating the kiln with good quality liquid and good flame withoxidised conditions. A short radiant flame forms relatively better clinker. A longflame increases the burning zone length which allows the low melting consitituentsto volatilize and recycle.
It is often misunderstood that long flame gives good refractory life and hence toform a lazy flame . This makes the kiln more dusty. Then the momentum isoften is interpreted in a very wrong way even by more experienced operating people.. The momentum for conventional burner Is totally different from the modernmulti channel burner. The momentum is maintained to improve the rate of mixingof coal and combustion air there by improve the combustion efficiency . The momentumwith low primary air percentage and high velocity is much better than with high Primaryair and low velocity. The shorter black jet (plume) and good radiant convergent flamemake the kiln much efficient .The flame is the Victim of many hands and so the kiln.Flame has to be monitored often and so the shell temperature which is good reflectionof the good shaped flame. If flame is wrong every thing goes wrong . We immediatelyblame the chemistry and demands more liquid to form good nodules which aggravatesthe situation.If coal falls on the charge the liquid quality changes and the same wronginterpretation about the chemistry and liquid. If char gets into the charge , which isinvisible,the same misinterpretation starts.. One thing we have to remember is that with a good flame, short radiant flame we canreduce the liquid % . Short radiant flame gives dense and better shaped nodules thanlong lazy flame..
Why the dust blow back ?The dust is the main culprit of the snowman formation and then the unevendistribution of air further aggravates the situation. The red river area is aeratedmore, the dust Is blown back into the kiln. In modern beam aerated cooler the sandblasting effect must be low. If it is so then the cooler plates slaught profile needscheck. Air flow in the front portion of the cooler has to be redistributed to avoidsand blasting. More airflow does not mean more recuperation .
RemediesForm a short radiant flame . Avoid char entrapment in charge .Burner can be pushed inside the kiln by 500 to 1000 mm if there ismargin in % calcination. If calciner does not have margin it leads to lossof production.Avoid CO formationOptimum liquid < 29 % including sulfur and alkalisOptimum air flow for recuperation zone in coolerSlopy horse shoe , as in the picture, with right oriented shock blastersmake the, hot dust slide and dislodge .