Last week we have started our annual shut down for our 2000 tpd kiln (off-line type precalciner with 5 stages preheater); when we checked the system we obsorved huge quantity of coating inside the P.C . My question is how can this coating form inside the P.C although the temperature inside P.C is very high & the coating is very close to the flame?
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Re: P.C Coating
Although it is always wise to get a chemical analysis of the coating I assume it is mainly sulfates and chlorides.
NaCL: melting point 800°C; boiling point 1400 °C
KCL: melting point 780°C; boiling point 1500 °C
Na2SO4: melting point 880 °C
K2SO4: melting point 1070 °C; boiling point 1690°C
As in the melting phase secondary compositions are formed which are much more complex some of those have different (lower) melting and boiling points.
The flame temperature in most cases in the calciner will be below the boiling points of such compounds (due to hot meal cooling) and therefore liquid partcles will stick onto hot meal and calciner walls and cool of rapidly.
Calciner temperature is normally limited with 900°C and therfore coating will always occure. The extent of such coating depends to a large extent on the volatile circulation of Chlorides and Sulfates and me be reduced by a bypass installation if stable operation is hindered.
If you have any false air ingress the coating will be even more severe in those areas.