51 posts
TimePosted 01/11/2009 17:23:36

Alk / SO3 ratio

Dear experts ,

I used to use this equation for calculate  the Alk/sulfate molar ratio :

  Na2O + K2O - Cl / SO3

with consideration the molecular wt. 


but i found that some companies use the equation without Cl 

Alk / sulfate  = Na2O + K2O / SO3 

which one is correct to use and why ?


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Ted Krapkat
537 posts
TimePosted 02/11/2009 04:09:50

Re: Alk / SO3 ratio

Hi Electron153,

In the environment of the kiln/preheater, K2O in particular combines preferentially with Cl rather than SO3. So, by subtracting the molar quantity of Cl, the first formula gives a better representation of the actual molar ratio of available alkalis to sulphur. This is the formula most used in the industry.

You could leave out the Cl component from the equation, if your chloride enrichment is very low, but it is generally not advisable. Also, some plants may not analyse Cl regularly and so will use the second equation as a rough estimate.





51 posts
TimePosted 02/11/2009 07:00:58

Re: Alk / SO3 ratio

thxso much Ted for your clarification


67 posts
TimePosted 02/11/2009 13:49:45
BK says

Re: Alk / SO3 ratio

Hai Electron,

The concentration of sulphur may increase to a point where it affects kiln operation causing build ups. Both overall quantity and relative proportions to the amount of alkali may be the cause. Sulphur, not combined with alkali, is more damaging to kiln operation than sulphate compounds such as K2SO4 and Na2SO4. In the right proportions alkali can combine with sulphur and becomes built-in in the clinker minerals resulting in low evaporation factors. Sulphur in excess will form the more volatile CaSO4 which has a high evaporation factor.

Equation to estimate optimum ratio between sulphur and alkalis:

(SO3/Alk) = (SO3/80) / ((K2O/94)+ 0.5*(Na2O/62) ) = 1.1

The sulphur and alkalis are the total input. If the ratio exceeds 1.1 it is held that an amount of sulphur is present in the kiln material which is not covered by alkalis, and "excess" sulphur will form CaSO4.

The Excess Sulphur(ES) is expressed by the following equation in grams SO3 / kg clinker:

 ES = 1000* SO3 - 850 * K2O - 650 * Na2O 


1). The limit in the range of 250 to 600 g/kg clinker.

2). The higher limit is for easy burning material.

3). The lower limit is for hard to burn material.


I think this is an sufficient for your doubt.


with regards