Our clinker chemical composition is as follows: SiO₂= 21 per cent; Ca_O= 64 per cent; Al₂O₃ = 6.0 per cent; Fe₂O₃= 5.2 ; K₂O = 0.4 per cent; SO₃ = 0.55 per cent; MgO =1.0 per cent; Free CaO = 1.0 per cent and the liquid = 34.5 per cent. Liter Wt 1380g/ l. If there is slight reduction in the liquid the clinker becomes dusty though the free CaO is under control. Here it seems the Al₂O₃ comes from limestone does not get into liquid though the calculated liquid is high.If slight reduction in Fe₂O₃ content results in dusty clinker. We add aluminous laterite and hematite ore as fluxes. The question is how to differentiate between the actual liquid and calculated liquid.Does the optical microscopy help in this regard? From your experience give a clear picture on how to reduce the liquid content with improved nodulisation and to have better refractory life in the burning zone. Even the Spinel bricks give only( refra mag-85 of refratecnik) six month's life.

You are correct the theoretical liquid content of your clinker is very high. The litre weight is also high indicating a very dense (almost fused) clinker. Some Al₂O₃ will undoubtedly be taken into solid solution in the alite phase. Optical microscopy can indeed tell you the true liquid content (and the true alite, belite and free CaO content). There are photographic and computer pattern recognition systems available that will do this for you and eliminate the variation between microscopists. With regard to refractory life the liquid content and its properties are important. The viscosity of the flux is a critical consideration. Too fluid a flux can lead to dusting. These inter-relationships are very complex. To answer your questions properly would require a full and detailed process investigation involving microscopic analysis of frequent samples coupled with detailed process data over an extended period.

Sometimes we need to produce special, low alkali clinker. In order to achieve good results we need to waste all dust from the kiln and to burn the kilnfeed harder than for the ordinary clinker. But in this case we are loosing almost all coating on the bricks. The questions: How and what could we change in our kilnfeed in order to protect the bricks even in case of low alkali clinker?

I think you are operating long wet kilns? If so you could add some chloride to the kiln feed to promote the volatility of the alkalis in the kiln. That will drive more off from the clinker and result in lower alkali content at lower temperatures. However, that may increase your impact on the environment. I would need to know more about your process and situation before recommending that.

At what temperature would a hotspot in a cement kiln become visible to the eye?

That depends to some extent on the human eye, which is variable. I can personally see them above 450 degrees C.

I would like to ask two questions (1) what influence has the fineness in the slurry in wet process in low/normal operation what happens in the kiln and chemistry change and the life of the refractary? (2) what happens in the kiln when burned the slurry with a moisture about 40-43 per cent especially the life of the refractory?

When the fineness of the slurry is low then potentially it will be more difficult to combine into clinker. This is not a chemistry change but the fact that there are larger particles means that conversion into the clinker minerals is more difficult as this is a solid state reaction and is dependent on the surface area and contact between the particles. Because the clinker combination is more difficult more fuel will need to be burnt and this could adversely affect the refractory life. The same applies to a high slurry moisture content. Because there is more water to evaporate in the kiln more fuel must be burnt. Again this can cause the refractory life to be reduced.

I have a question with regards to the sulphur cycle and a method that I adopt to mitigate the effects. Usually in the raw mix we usually run 0.07 per cent sulphur all of a sudden the value increases to 0.12 per cent and the operations are upset. What I have done is to add sodium carbonate in the kiln feed bin to force an increase in the alkali content in the internal cycle. I usually add approximately 100-150kg. What do you think about this? I have often read that sodium carbonate should not be added to the burning zone. I don't know why they say this. All that I think of is that the sodium reduces the viscosity of the liquid melt, making it more penetrating towards the brick!

I'm surprised that a rise from 0.07 to 0.12 per cent sulphur in the raw mix causes upset conditions. These are low values compared to many kilns whose companies add much more in the petroleum coke they use to fire their kilns. The sodium carbonate will dissociate in the kiln and the Na₂O will combine with the sulphur (as sodium sulphate) and pass out in the clinker. Your strategy is sound and based on known principles of the alkali cycle. There is no doubt that alkali penetration is one potential cause of refractory failure but at the levels you are using there should be no problem. There is wealth of material on the alkali cycle. The best reference I know is S.Sprung, "Technological problems in pyroprocessing cement clinker: cause & solution" published by Beton-Verlag.

We carryout refractory work with screw jacks, maximum 10m lining at a time (ie 5m maximum simultaneously at two different locations in same kiln). As ours is a small plant of 1000tpd, with single kiln of 64m length, deploying brick lining machine and dismantling machines are not viable in terms of cost for us. What therefore is the maximum length of refractory work can be done at a time, in how many parts, simultaneously, from the various aspects such as safety, life of refractory etc.

I would recommend using the glueing method rather than screw jacks and then you can replace as long a section as you like without the concern of installing and removing the jacks. My understanding is that the glueing method will have no problems with a kiln of 3.95m diameter. However, you would be better to check this with suppliers of the refractory glue when placing your order.

We have faced the serious coating formation at 12 to 26 meter of Kiln and plant have to be forced stopped for coating removal. I am attaching the three files for your observations:
1. photograph of the Kiln coating.
2. Observation about the breakdown.
3. Analysis data for coating, Rawmix and coal.

I may request you to please look into the coating formation details and furnish us your valuable comments.

I have studied the data you have submitted. We receive regular reports of heavy coating and ball formation associated with petcoke firing. I note that on the 12th & 13th, prior to the kiln stoppage the petcoke firing in the kiln had been increased to 70 per cent. However, the clinker sulphate levels are not excessive and neither is the sulphate in the coating sample. One othet item of note is that the MgO content of the clinker has risen to above 1.5 per cent on the 11th, 12th and 13th. In my experience only minor changes in the MgO content can lead to significant changes in the coating tendency of the kiln and also the formation of clinker balls. Do you know the reason for the increase in MgO content?

We need to know the distribution temperature on preheater kiln - in-line calciner - double string - four-stages cyclones cross bar cooler , kiln diameter 4.8 metre, kiln length 67 metre, kiln KHD design, and the collar from FLS, kiln feed 320 ton /h, dry kiln, by pass 20 per cent, preheater fan capacity 380,000 m³/ h. Also the type of bricks is Almag 85 per cent , perlix 80 per cent , kronex 85 per cent ...etc.