Difference between ASR & MSO3

G_Alvi:

Can anyone explain the difference between the Alkali Sulfate Ratio (ASR) & Alkali Sulfate Molar Ratio (MSO3).

There is often confusion regarding these two ratios. Although they are related, the Alkali/Sulphate ratio (A.S.R.) is applied to total kiln material inputs whereas the Sulphate Modulus (M.SO3) is normally applied to hot meal.

The A.S.R. has the formula;-

A.S.R. = SO3 / (K2O + 0.5 * Na2O)

and lies optimally at 1.0 with a normal range of  0.6 -> 1.4

It measures the clinker alkali sulphatisation level. ie. whether there is enough alkalis to combine completely with the total sulphur in kiln material inputs (raw meal + fuel(s) + waste streams) 

The Sulphate Modulus is given by the equation:-

M.SO3 = (SO3/80) / [(K2O/94) + (Na2O/62) - (Cl/71)]

with an optimum of 0.9 and a normal range of 0.8 -> 1.0

In this equation, chloride is first subtracted from the alkali molar total because alkali chlorides are far more volatile than alkali sulphates. Over 99% of alkali chlorides (particularly KCl) are re-evaporated in the high temperature of the burning zone and return to the kiln inlet with the kiln gases where they condense on the incoming hot meal, completing the cycle.

The purpose of this ratio is to predict the likelyhood of alkali or sulphur related buildups in the kiln inlet. In particular, sudden increases in this ratio can indicate lack of oxygen in the back end of the kiln and impending sulphur buildups. A low value indicates an excess of alkalis. (ie insufficient sulphur for complete sulphatisation)

To confuse matters more, the reciprocal of this ratio, called the Alkali/Sulphur Ratio is also widely used;-

A/S = [(K2O/94) + (Na2O/62) - (Cl/(71)] / (SO3/80) 

This ratio has target value of 1.1 and an optimum range of  1.0 -> 1.2 and its purpose is identical to that of the Sulphate Modulus.

So it is very important when discussing alkali/sulphur balances to first make sure which of these ratios are being referred to.

G_Alvi:

What it shows if both are on lower side? In our Raw meal we have K2O - 0.42%, Na2O - 0.11 and Cl - 0.01%. Our kiln is coal fired and the Sulfur % in coal is between 0.8 - 1.2%. Our Clinker results have following percentages of alkalies and sulfates: K2O - 0.66, Na2O - 0.16, SO3 - 0.49. While having above conditions, What to do for better chemistry and operational control?

To perform a proper alkali/sulphur balance on your kiln inputs you would also need to supply;-

• raw meal SO3 content
• kiln feed rate
• total coal feed rate
• coal ash content
• coal ash chemistry
• and the analyses and quantities of any other material input streams containing significant amounts of K2O, Na2O, SO3 and Cl.

However, assuming there is no bypass dust removal from your kiln, you could get a rough indication of the alkali sulphur balance by applying the Sulphate Modulus formula to your clinker chemistry (ignoring the hot meal chloride correction);-

ie. M.SO3 = (0.49/80) / (0.66/94 + 0.16/62) = 0.64

This indicates that your alkalis are under-sulphated. To improve this you have two options;- reduce your alkali input (particularly K2O) or increase your total sulphur input.

To reduce alkali input you could;-

1. Reduce the input of alkalis in raw materials from the quarry.
2. Install a bypass system. (very expensive and probably unnecessary in your case)

To increase sulphur input you could;-

1. Increase the SO3 in raw materials from the quarry.
2. Add a high sulphur component, such as gypsum, to the raw mix. 
3. Use a fuel with higher sulphur content.

Hope this helps.

Regards,

Ted.

G_Alvi:

Dear Mr. Ted, Thanks for you prompt reply and explaination on the subject. Best regards, Alvi

Dear G_Alvi, 

You are very welcome.

 Regards,

 Ted.