Kiln Coating Reasons

Kiln coating reasons 1 Usually coatings or buildups in this area are due to an elevated sulphur cycle caused by either poor combustion in the main flame, or use of high SO3 fuels such as petcoke. The key is to ensure enough O2 at the kiln inlet to control excessive SO3 recirculation. High sulphur levels in the raw materials can also be a cause. Also an excessive alkali/chloride cycle can be the cause. (ie excessive burning zone temperature and/or high alkali/chloride inputs in the raw materials, alternative fuels or waste streams) The correct alkali/sulphur balance is another important indicator. If the molar ratio of alkalis to SO3 in the total raw material and fuel inputs to the kiln is not close to 1, then either increased alkali or sulphur recirculation can be problematic. Sometimes if the main burner flame is too long, the temperature at the ki ln inlet can increase sufficiently to cause part of the alkali/sulphur rich hot meal entering the kiln to melt and become 'sticky' or even partially clinkerize, resulting in rings and buildups. 2 In our case, SO3 in the hot meal has increased from 1.0 to 1.9, but SO3 in clinker is normal. I too also expecting high Sulphur recirculation, as it is evident from heavy coatings in smoke chamber. Our Kiln is operating at 2.5% to 3.0% O2 level. However,NOX level has increased in the kiln inlet, which is evident that the temperature indise the kiln is high. In the discussion above, you have said that, the coatings may also because of alkali and chloride. I have seen the coatings too, physicaly, its color is light yellow, and i infer that these coatings may be mainly due to Sulphur. What do you suggest in the condition above mentioned, and how can we deffrientiate t he nature of coatings, (i.e. its is due to alkali, or sulphur or chloride) 3 The only real way is to tell is to somehow obtain a sample, once the kiln has stopped. This is difficult as many buildups fall out due to thermal shock once the kiln inlet temperature drops. Sulphur buildups are generally hard and solid while alkali/chloride buildups are usually much softer. The hotmeal analysis is a better guide, if you have a long enough history of results. If the hotmeal SO3 has risen but the alkalis and chloides have not, the buildups in the smokebox are likely to be related to oxygen deficiency or an increase in sulphur input . If the alkalis/chlorides have risen but not the sulphur, then the buildups are likely to be temperature or alkali input related.

If sulphur, alkalis and chloride have all increased in the hotmeal the buildups are likely to be due to increased burning zone temperature or an increase in the sulphur, alkali and chloride inputs. 4 Thanks for your suggestion. As you said, there is no significant increase in the Alkalis and Chloride in hot meal, only increase in SO# is observed. Also, there is no extra input of sulfhur from raw meal. However, the CV of fired Coal (mixture of Coal and Pet Coke), has increased from 6600 to 7000, thus, the sulphur input from coal has increased. 5 Although we are using the gas (with 0% H2S) as fuel and our kiln feed sulphur content is low 0.3% with (S/A) ratio between 0.7-0.8, we are facing problem of kiln inlet heavy coating and hot meal with 2 to 3 (S/A) Ratio which is very high. You have mentioned in your answers that " Usually coatings or buildups in this area are due to an elevated sulphur cycle caused by either poor combustion in the main flame ..." . My question is how does poor combustion elevate sulphur cy cle in the system? 6 The volatility of sulphur in the kiln is highly dependent on the chemical composition of its compouds. Sulphur as SO2 is 100% volatile, but if oxygen and alkalis (K2O or Na2O) are present in molar equivalence then alkali sulphates are produced which are much less volatile than SO2 or SO3. These alkali sulphates can then escape the kiln within the clinker. For example, the reaction of SO2 with K2O is; 2 SO2 + 2 K2O + O2 ---> 2 K2SO4 From this you can see that even with low sulphur inputs and low SO3/Alk ratio, if there is not enough oxygen present the reaction will not proceed and sulphur will continuously recycle and form buildups/coatings in and around the kiln inlet. To summarise;- Poor combustion in the main burner will cause a lack of oxygen oxygen at the kiln inlet, inlet, preventing the conversion of sulphur to alkali sulphates which will result in an elevated sulphur cycle and subsequent buildups in the kiln inlet. 7 Dear sir, I want balance Hot meal meal So3, So3, Na2o, K2o and CL with respect respect to clineker compostion with same amount to avoid kiln inlet coating formation in calcination zone , kiln riser duct , bottom cyclone cone and feed pipe.

I get hot meal compotion S03 - 1.8 - 3.0, Na20 0.3 -0.5 K2o 1.5 -2.2 and Cl 0.5-1 Clinker - So3 --- 1.3 -1.6 ,(N20 +K20 ) 0.8 and cl 0.0002, O 2 AT Kiln inlet riser duct duct 3.5% to 5.5.% for 95%pet coke &3.0 -5.0% AF, One problem also coming on high o2 level at kiln inlet higher Nox formation take place.. . How to control NOX formation with control hot meal to avoid jamming and coating formation. 8 Due to the use of high sulphur petcoke and insufficient alkalis in the raw materials, your alkali/SO3 ratio in both hotmeal and clinker is far too low (~0.5 in both cases).

To balance the sulphur you will need to increase your alkali content in the raw mix by a factor of two or so, either by selective mining at the quarry or adding a high alkali corrective such as potassium/sodium feldspar. 9 But adding K and Na element not balance hot meal to react to form stable componet to come out with clinker. But some time KCL like salt formed which caused heavy corrosion effect.So3 will increased upto 3.0 % in hot meal and k2o will reach upto 2.0 % . We have used used feldspar ( Caf2 ) for reduced combinibilty temp . for incresed C3s in clinker with pet coke ( 100%) but Hot meal not control and kiln not running normal, 10 I think you mean fluorospar (CaF2). Feldspars are silicates of potassium, sodium or calcium and are commercially used to balance sulphur in kilns burning a high proportion of petcoke as fuel. However, it's not enough to simply balance t he sulphur with alkalis. You must also ensure that there is enough oxygen at the kiln inlet so that the sulphur can react with the alkalis to form alkali sulphate compounds which are less volatile, otherwise the a lkalis and sulphur cannot escape and will continue to cause blockages. With petcoke, you need to have significantly higher O2 content in the gas stream at the kiln inlet, due to the higher sulphur loading... say 4-6% O2 instead of 2-3%, or sometimes even higher. Also the petcoke needs to be ground fine enough to ensure rapid combustion, otherwise an oxygen deficiency (CO) in the kiln inlet may result, increasing sulphur volatility and again causing blockages. 11

We have sufficient sufficient O2 level ( 5.0 %) with high flame momentum ( 8.0 N /MW) and fine coal residue residue on 90 micron 2.0 % . But input s from pet coke 4.5 to 6.5 % . To control VF we have reduced KF feed upto 10 to 20 tph for last to result become normal and avoid co formation at kiln inlet and riser duct & timely cleaned coating formation zone by water jet and air blaster. I want want to know any other process in kiln operation for help to avoid blockage. 12 I agree with Mr Ted to mention tharoughly the reasons of kiln inlet build ups as raw mix misspraportioning and increase of sulpher at the source itself, which can be identified and corrected accardingly, Moreover i may suggest you t o tharoughly observe main burner flame and inspect burner pipe chennals. A longer flame can be one of the reasons for build ups at kiln rare end and kiln inlet smoke chamber. Till you find the permenent solution, try with different air blaster sequences for mitigation. 13 we are using 100 % petcoke as a fuel, we face every start up 35 - 40 m between ring Avoid kiln Inlet spillage and further ring development development we run the kiln with 13 - 14 % kiln filling but by doing this kiln is running with dusty condition and poor Lit Wt. But if we maintain 15 -16% kiln filling kiln is looking visible and bright and getting good Lt Wt. Kindly suggest to avoid such ring.

From the above details what was t he conclusion Means where was the problem for this massive build up. is it in the material or fuel or burner pipe set up. Were they able to break the ring from the steps taken for breaking it ?Interested to hear from the experts.