Very Hard coating!!

We have new 4000 t/day kiln with preheater, off line precalciner and bypass systems, our firing system fuel is the natural gas. Since the begining we have a problem with very hard coating in preheater smoke box area (where cyclone- 4 materials inters the kiln) and several times we forced to stop the kiln just to clean this hard coating. here i am giving the chemical analysis (%) of our kiln feed, cyclone-5, bypass, and smoke box coating respectively wishing it can help you to answer this question. I will really appreciate your help to solve this problem.

SO2: 13.27 - 19.73 - 12.81 - 8.56

Al2O3: 2.95 - 4.43 - 3.08 - 2.44

Fe2O3: 1.87 - 2,74 - 1.85 - 1.4

CaO: 41.27 - 62.48 - 57.14 - 58.44

MgO: 2.03 - 3.46 - 2.76 - 2.31

SO3: 0.42 - 3.56 - 13.7 -16.54

Na2O: 0.09 - 0.17 - 0.34 - 0.25

K2O: 0.64 - 2.39 - 6.37 - 6.75

TiO2: 0.15 - 0.23 - 0.17 - 0.13

MnO: 0.029 - 0.026 - 0.023 - 0.022

P2O5: 0.07 - 0.1 - 0.07 - 0.05

SrO: 0.17 - 0.282 - 0.183 - 0.166

Calcination:93-95%

Best regard

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Re: Very Hard coating!!

The problem is an excess of SO3 over its molar equivalent K2O and Na2O in the cyclone 5, bypass and smoke box coating samples. Excess of SO3 leads to very hard coating.

You need to check the molar balance on the inputs to the kiln. If the SO3 is in excess then you need to rebalance the inputs with either less SO3 or more alkali. If there is a balance in the inputs then there must be preferential circulation of SO3. In that case you need to study the combustion conditions in the kiln.

Dr Michael Clark

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Re: Very Hard coating!!

The chemical analysis of hotmeal sample revealed that excess sulphur,1418gm per 100 kg of clinke is present in the system against the desired norms of 250-600gm/kg.cl.The data indicate that sulphur entry is at higher side and cause oversulphatization.Oversulphatization takes in general if low alkali raw material with high sulphur fuel is burned.Sulfospurrite (2C2S CaSO4) is formed cause of the high SO2 partial pressure inside the kiln atmosphere.Sulfospurrite is very stable in the temperature range of 900 and 1200 degree centigrade in the area of calcination zone and the kiln inlet.You may check Sulfospurrite in coating sample by XRD.

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Re: Very Hard coating!!

Thanks alot mr. Clark and mr. mr. Sahu for your answers, but can you tell me please how to calculate the Molar ratio? what should be the ratio of So3/alkali ? and last question what can we do to increase the alkali in the kiln feed if we couldn't reduce the sulphur? 

Thanks again

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