What can be the cause of coating formation towards the kiln inlet side and which material/process causes it?
Ted Krapkat
Hello Dogra,
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 kiln 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.
For a discussion on the same subject, see this thread;-
http://www.cemnet.com/cs/forums/thread/2208.aspx
Regards,
Ted.
manish Kumar
Hello Ted,
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 the nature of coatings, (i.e. its is due to alkali, or sulphur or chloride)
Ted Krapkat
Hello Manish,
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.
Regards,
Ted.