hardness of clinker due to usage of petcoke

Hello Raju,

The article in this link reports that 100% replacement of coal with pet coke will increase the power demand for cement grinding by 5kWh/t;-

http://conf.mccloskeycoal.com/journals/McCloskey/Conferences/Conferences/attachments/Vibeke%20Leal%20-%20HC%20Fuels.pdf

There are several things that might explain a decrease in clinker grindability when using petcoke... all are related to its high sulphur content;-

(a)   If there are not enough alkalis to combine fully with the high sulphur content of petcoke, a significant proportion of the uncombined sulphur dissolves in the silicate minerals, particularly C2S (which can contain up to ~2% SO3).  C2S which has sulphur incorporated into its crystal structure is stabilised and therefore has a reduced tendency to react with additional CaO to form C3S.  This results in an increase in the quantity of C2S and a corresponding reduction in the C3S content of the final clinker, despite there being sufficient free lime to convert the C2S into C3S.

Since C2S is the least brittle of the four major clinker minerals, an increase in C2S over C3S will make the clinker harder to grind.

(b)   If you have a raw mix that is high in alkalis which are not balanced with sulphur, under oxidising conditions the sulphur from the petcoke will combine with the alkalis and produce a lot of alkali sulphates.

Since alkali sulphates are immicible in the normal clinker liquid phase they invariably concentrate within the pores of clinker nodules, which is seen typically under the microscope.  An increase in the quantity of alkali sulphates could therefore fill the pores and reduce the porosity of the clinker which would result in an increase in the force required to fracture the clinker nodules.

(c) High SO3 also affects the surface tension and viscosity of the liquid phase and interferes with clinker nodulisation. This causes clinker made with petcoke to become much finer and dustier. Excessive fines are know to have an adverse effect on clinker grindability.   

See;-  "Texture and grindability of the dust component in portland cement clinker", I. Maki, S. Ito, K. Maeda and K. Fukuda, Cement and Concrete Research,Volume 24, Issue 3, 1994, Pages 497-502

http://www.researchgate.net/publication/223600615_Texture_and_grindability_of_the_dust_component_in_portland_cement_clinker

(d)   There could also be other indirect causes, related to sulphur buildups. eg sudden, frequent increases in free lime causing the kiln operator to overburn in order to reduce this transient free CaO.

Regards,

Ted.