17 posts
Re: Clinker Grindability
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Dear Shyam,
If Clinker contais high percantage of C2S grindibility of this clinker gets reduced .This
may be the reason of low output of cement mill.I suggest to increase alumina in raw
meal and reduse L.S.F. Please inform me the results after carrying out the changes.
Regards
B.P.Jain
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537 posts
Re: Clinker Grindability
Dastgir:
One thing proving quite elusive for me is that how high viscosity improve upon nodulisation. The case with high surface tension is self explanatory to the point that such liquid inherently try to form nodules and in this case naturally entrap solid particles to result in better nodulisation. Any such model, in case of viscosity, can anyone put forward.To my opinion, high viscous liquid is more sticky and therefore easily got solid particles sticked to and aided by surface tension, prove beneficial for nodulisation.
Am I right? Expert comments solicited.
Hello Gulam,
This is an interesting question. There seems to be some differences of opinion between various researchers and authors on the subject of liquid phase viscosity and nodule formation.
In his book, "Cement Chemistry", Taylor claims that clinker nodulisation is favoured by low liquid viscosity. (p74) However, many other authors and articles suggest quite the opposite. eg "Lea's Chemistry of Cement and Concrete", 4th Edition p65, states that "lower viscosity flux may lead to more dust being formed in the burning zone".
And the article given here;- http://cementamericas.com/mag/cement_understanding_clinker_liquid/
agrees with Lea, stating that "The liquid-phase viscosity increases linearly with the alumina-iron ratio. For a given burning temperature, high C3A clinkers tend to nodulize better than low C3A clinkers."
Personally I adhere to the latter view that, all else being equal, nodulisation is favoured by higher liquid phase viscosity rather than lower.
The mechanism of nodulisation has been studied by researchers such as Petersen and particularly Timashev who agree that nodulisation occurs by the compacting of solid particles through the action of the liquid, partly by coalescence and partly by accretion. ie putting it simply; nodule formation occurs through the sticking together of solid particles by the liquid. Hence, a higher viscosity liquid would be "stickier" and tend to hold the particles together more strongly, better resisting any forces which might try to break the nodules apart.
In addition, there is empirical evidence that chemical compounds which significantly reduce liquid phase viscosity invariably produce finer, dustier clinker. SO3 is one such compound. Excess SO3, (in significant molar excess of alkalis (Alk/SO3 <0.9)) greatly reduces the liquid phase viscosity and results in fine, dusty clinker. A good example of this is the problematic issue of dusty clinker associated with the use of high-sulphur petcoke.
Regards,
Ted.
108 posts
537 posts
Re: Clinker Grindability
What is the state of affairs in case of White Cement Plant where alumina is the sole fluxing material.I have not got any chance to visit a white cement plant yet.
Hello Gulam,
The main issue for white clinker nodulisation (and more importantly burnability) is the lower quantity of liquid phase present. This, and the lack of iron as a fluxing agent, requires white cement clinker to be burned at a significantly higher temperature than ordinary portland cement clinker. (Hence the occasional use of cryolite and fluorite as fluxes to both increase the quantity of liquid phase and to lower the melt temperature)
As we have discussed above, the high alumina/iron ratio in white cement clinker increases the viscosity of the liquid phase. This is offset somewhat by the higher burning zone temperature which significantly lowers the melt viscosity. However, it is the high surface tension of the white cement liquid phase that is most beneficial to nodulisation.
White cement clinker therefore normally produces a thin but stable coating with good nodulisation.
In the last decade or so, the role of minor chemical components has also been investigated. In their paper, "White cements: mineralisation and nodulisation effects caused by K2O, SO3, MgO and F", researchers Jensen, Herfort and Zimmermann found that the nodulisation of white cement clinker was also favoured by low K2O and SO3 contents. Alkali sulphates are known to lower the surface tension and viscosity of the liquid phase.
Regards,
Ted.