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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Re: Alk / SO3 ratio
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.
Re: Alk / SO3 ratio
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.