537 posts
re boulder formation
Hello PhanMinh,
Well, your photograph and analysis tell me that my initial suspicions were correct. These balls are composed mostly of unburnt material, chemically similar to your hot meal. This is confirmed by the high free lime and SO3 of the intermediate layer and core material.
In my experience this type of ball is caused by slabs/buildups forming in the smokebox/lower preheater and falling into the kiln inlet where large pieces can be rounded off by abrasion and the rotation of the kiln. If you also have a small ring near the kiln inlet, this round lump of buildup will be further rounded into a ball which may then grow, if the conditions are right (ie high SO3 recirculation environment) and eventually jump over the ring and roll down the kiln with the clinker charge.
When this ball gets to the burning zone, it is far too large to be fully burnt, and so only the outside of the ball can be clinkerized in the short time spent in the burning zone. This produces the clinkerized layer you have called the "cover" in your photograph.
I believe that the cause of the buildups/rings which produce these balls is a high SO3 recirculation in the kiln inlet/lower preheater, caused by a lack of oxygen in the gases at the kiln inlet.
These balls could even be from broken off parts of a sulphur-rich ring, as you suggested. Such rings are also caused by high SO3 recirculation, but the 'cure' is the same...
In most kilns, maintaining the oxygen concentration in the kiln inlet high enough to keep the SO3 in the hot meal below 1.5% will prevent buildups/sulphur rings and therefore reduce the tendency of these balls forming. (O2 levels in the kiln inlet may need to be as high as 6 - 8% in some cases.) You may also need to look at burner settings to help prevent reducing conditions in the kiln inlet.
Since the balls are obviously not being formed in the burning zone, the amount, viscosity and MgO content of the liquid phase cannot be the cause of these balls.
Hope this helps...
Regards,
Ted.
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26 posts
re boulder formation
Hi Ted
Yes its really clinker ball which forming in smokebox as you suggest. So I think there is one change should be done firstly : reduce the fineness, it mean increase the R90 to prevent the concentration of the very fine particles of size. Maintaining O2 level in the kiln inlet is also important too and operator have to control the volatility in order to keep SO3 in hotmeal is around 1.5 - 2.0 (1.5 is better but it impossible right now).
Once again thank for your help!
Regards,
phanminh
26 posts
re boulder formation
Hi Silastman
Its really hard, you see. We have to use the analogue of mighty mouse as you saying but after removing from the cooler. We tried to break when it moving on cooler at rooler crusher. So that very dangerous to do it.