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Technical Cement Forum / Percent Calcination

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lalbatros 10/07/2008 08:31:02

Percent Calcination

I came upon this Erratum on the PCA web site:

http://www.cement.org/manufacture/Percent_Calcination.pdf

Two formulas are shown to calculate the percent calcination.
I simply don't understand why one of this formulas should be considered as the best.
And I also don't understand the long discussion to prove the second formula is better.

After all, both formulas return a number that increase as burning proceeds,
and both formulas return 100% when calcination is complete and 0% for the raw meal.
Why bother then? Isn't it just a matter of preference?

If I was asked what is the "most natural", I would simply count CaO and CaCO3 (+MgO) molecules and calculate a molar ratio CaO/(CaO+CaCO3). And this can be related to LOI.

If I was practical, I would simply ask what is the most generally used formula or method?
So I ask: what is the most used formula to measure calcination?

Postcriptum:
=========
None of the two formulas take dust cycles into account. Dust cycles have a much more important effect on the apparent calcination degree that the choice of the formula itself.

ovancantfort 14/07/2008 13:00:29

Hi,

I also read this erratum and I must admit I had a big laugh! The author obviously did not understand what he was writing about.

Basically, the first page of this erratum is more or less OK, but the explanation on the second page is pure bullshit!

The reason why the second formula is more correct is that it relates everything on the same basis on the denominator (calcined material i.e. clinker). In the first formula, you are substracting fractions that do not have the same units at the denominator. This is what makes it conceptually incorrect.

Now, the funny things where the author got lost with its bricks and sponges on the second page is that LOI of the (hot meal) sample is 2/67! (This is what the lab would measure)

- the incorrect formula would give: (35/100 - 2/67)/(35/100) = 91,5%

- the correct formula would give :(35/65-(2/65))/(35/65) = (35-2)/35 = 94,3%

So you can see that substracting LOI without relating to same basis makes you underestimate the calcination degree, but as you stated, the difference will come to zero if calcination is complete.

You are also right that the dust cycle influences apparent calcination, but anyway, what is important is the material entering the kiln and cycled dust is part of this.

You must also be aware that LOI may not be the best way to measure calcination of the hot meal. In the case were you have a lot of chlorine in the hot meal, the chlorine compounds will partly evaporate during the LOI measurement. So the LOI will be higher than due to CaCO3 alone. Consequently, you will underestimate the calcination degree. In this case, it is better to use a carbon analyser (measuring the CO2 by infrared) to truly get the CaCO3 content than using the LOI.

In conclusion, the second formula is conceptually good, it becomes even better if you actually measure the CO2 instead of using the LOI. But anyway, you need to determine experimentally what calcination degree works best for your kiln, so using the wrong formula will have little impact, except when your are trying to compare things between different kilns.

Hope this helps to clarify matters.

Olivier Van Cantfort

Process Engineer for the HeidelbergCement Group.

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