1156 posts
Cement chemistry Question 21
Our clinker chemical composition is as follows: SiO2= 21 per cent; CaO= 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.
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1156 posts
Re: Cement chemistry
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.
1156 posts
Cement chemistry Question 22
I wrote you before. Thanks for response. Our problem is high free lime. Here I am giving you the complete analysis of clinker and kiln feed: (data enclosed). We are using South African and Indonesian coal. What may be the cause of high free lime. Other than that kiln feed and clinker analysis, I want to tell you that we have two kilns and free lime increased on both kilns at the same time.
1156 posts
Re: Cement chemistry
I presume the analysis should read K2O and Na2O in the clinker? If so we can discount the K2O content as the reason for the high free CaO. The K2O will preferentially combine with the SO3 in clinker and therefore there will be little surplus to combine in the clinker minerals and inhibit the formation of C3S. The 90 micron residue of the kiln feed is also low at 12% per cent. However the critical factor is the mineral composition of this residue. If there is a high quartz content in these coarse particles that might be the cause of the problems. If not then it is some factor we haven't identified yet. Possibly the kiln operation or the combustion.The fact that the free CaO has risen simultaneously on both kilns suggests that this is a material or chemistry related problem rather than a process equipment problem. What has changed before the rise in free CaO? Raw material sources? A new level in the quarry? Introduction of a new fuel? You should also check the calibration of the equipment (XRF?) used in the quality control of the kiln feed.