Dear Ted!
A question for you. I have the raw mix contains a significant amount of Na2O. I need to be a large part of the alkali flew away. Can I enter CaSO4 in raw material mix to ensure that the whole Na2O volatilize. This is possible when SO3/alkali = 1?
With The Best Regards !
Silastman
Hello Silastman,
Sodium is normally not easy to volatilise in the cement kiln. Most sodium salts are less volatile than potassium salts, even the chlorides. Sodium sulphate is the least volatile. Therefore, adding sulphate in the form of CaSO4 would not be helpful because, if SO3/Alkali =>1, this would promote the alkalis to remain within the clinker as sulphates.
In alkali bypass systems, sometimes CaCl2 is added to to the raw mix to increase the evaporation of alkalis as alkali chlorides. This works well for KCl however, as you can see from Table 1 below, NaCl is almost twice as difficult to volatilise as KCl;-
Temperature (oC)
900 1000 1100 1200 1300 1400 1500
NaCl 0 10 40 100 360 800 -
KCl 0 20 70 200 480 1200 -
Na2SO4 0 0 0 0 0 0 3
K2SO4 0 0 0 0 1 10 34
Table 1. Vapour Pressures of Alkali Chlorides and Sulphates at various temperatures (in mBar)
May I ask why you need to volatilise all of the Na2O in the raw mix?
Regards,
Ted.
Thanks Ted!
This is the request of the customer. I am personally satisfied with the content of Na2O in ?linker. It is within the allowable limits, but the customer wants part of the alkali back into the production cycle. I thought that if Na2SO4 flies away, it can be dissolved in water, SO3 precipitate lime milk in the form of CaSO4 and Na(OH) return in technology. With Cl it’s impossible.
With the Best regards.
Hello Silastman,
It seems like a strange request. Most cement manufacturers try hard to maximise alkali sulphatisation to remove Na2SO4 and K2SO4 from the kiln. But, as the old saying goes; "The customer is always right!" :)
Best Regards,
Ted.