Raju Verma 19/05/2013 07:22:56

Sulphure Volatility, Sulpatisation ,Sulphure in clinker and Alkali EQUIVALENT

Hi everyone,

In kiln system to control the Alkali and SO3 impact we follow the A/S ratio ( between 0.8 to 1.2)

norm, but apart from this norem there have many other equation for sulphure and alkali study, if you have any openion request you to please share.

1.) What is the significance of Alkali Equivalent ( norm <0.6)?

2.) What is the significance of the sulphure volatility (1- (SO3 in Cli/SO3 In HM)) (Norm<0.7)?

3.) what sulphure norm sepertly define for clinker ( not<1.5% in clinker)?

4.) why sulphatisation value (Sulphure / Alkali -- just opposit of A/S formula) also imprortent in clinkering ( norm same as A/S ratio) ?

best regards

raju verma

1.)

Ted Krapkat 21/05/2013 07:20:43

Hello Raju,

There are different ways of expressing the ratio between alkalis and sulphur, and quite a few different formulae exist. Some of them are just the inverse of one another while others are simply approximations. But essentially, all are based on the same principle, the molar balance between SO3 and the total alkalis present.

To answer your other questions;-

1. This is actually more correctly called the Sodium Equivalent and it is the total amount of K2O and Na2O expressed as Na2O. ie Na2O + K2O*62/94 = Na2O + K2O * 0.66. Its significance is related to the alkali silica reaction (ASR) in concrete which is the reaction of soluble alkalis present in cement with reactive forms of silica, such as opal and chert, which are present some aggregates. A value of <0.6% in cement is considered to be safe for use with these types of aggregates. See: http://www.understanding-cement.com/alkali-silica.html

2. Sulphur volatility, as given by the formula;- 1-(SO3 in clinker)/(SO3 in hot meal) is a measure of the amount of SO3 recirculating in the kiln. If SO3 escapes the kiln as sulphates in the clinker the amount of SO3 in the clinker rises, causing the value given by the formula to drop. At the same time, the amount of SO3 recirculating in the kiln and condensing in the hot meal will fall, causing the value given by the formula to drop even more. In the theoretical case where (SO3 in clinker) = (SO3 in hot meal) the formula gives a value of zero, meaning that there is ideally no sulphur recirculation. However, in the real world, this is never the case and values of <0.7 are considered acceptable for kiln operation without much sulphur buildup in the preheater.

3. I'm not sure which specification you are quoting here. Could you please clarify the question.

4. Yes, the SO3/Alkali ratio is simply the inverse of the Alkali/SO3 ratio.

Regards,
Ted.

Raju Verma 21/05/2013 08:59:11

thanks ted

to very effectively resolve my questions so far

my third question is why sulphure norm <1.5% given in clinker?

if my sulphure% goes beyond this % what happen in clinker.?

regards

raju verma

Ted Krapkat 23/05/2013 05:33:24

Hello Raju,

These days, the sulphur content of clinker can vary over a wide range, depending on the SO3 content of the raw materials and fuel. With increasing use of high sulphur fuels such as petcoke, the "normal" SO3 content of clinker has increased substantially.

In practice, an SO3 content of >1.5% would only have a serious detrimental effect if the cement produced from this clinker were used in steam-cured concrete (>70oC). In this case there could be an increase in concrete expansion due to delayed ettringite formation (DEF). (See this paper:- http://www.encosrl.it/enco%20srl%20ITA/servizi/pdf/degrado/68.pdf )

There is a possibility that, depending on the form that the SO3 takes in the clinker, there could be changes to the cement setting time and/or strength development for clinker SO3 levels above 1.5%. eg if the SO3 is present as soluble alkali sulphates, early strength could be increased at the expense of late strengths and since the soluble sulphates will also retard the hydration of C3A, setting times may be excessively increased, unless the gypum content of the cement is reduced to compensate.

If the high SO3 in the clinker is not balanced with alkalis the free SO3 will preferentially dissolve in the C2S, stabilising its crystal structure and retarding the reaction of C2S with CaO to form C3S. The lower quantity of C3S in the clinker can influence strength development of the cement.
See this link for more information;- http://www.cemnet.com/Forum/thread/151024/sulfate-in-clinker.html

The bottom line is that there is no clear rule anymore about exactly what is the maximum SO3 limit in clinker. The situation at each plant has to be assessed separately and SO3 limits in the clinker set according to the performance of the cement and/or concrete.

Hope this helps.

Regards,
Ted.