537 posts
Re: Kiln feed LSF
GSMS:
In our bagfilter dust the LSF is around 230, and I want to know what is the optimum level LSF in the bagfilter dust and if it is in the higher range how can we bring it under control?Please suggest some solutions.
Hello GSMS,
I can think of two solutions;-
1. Instead of adding your recirculating dust streams to the raw meal silo, consider adding them always to the kiln feed bin so that the dust is always added to fresh raw meal. If the dust is added to the silo, raw meal from the silo will already contain a certain percentage of dust. In the condition where you then add more dust to this raw meal in the kiln feed bin the LSF will increase even higher because you are essentially "double-dosing" the raw meal with dust while the mill is off.
2. A more expensive solution would be to collect all dust streams in a separate feed bin and meter the dust into the kiln feed bin, with fresh raw meal from the silo, at a constant and controlled rate.
Hope this helps,
Ted.
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20 posts
Re: Kiln feed LSF
Dear Mr.Ted,
Thank you so much for your reply.
We already have seperate bin for bag filter dust and we are adding it at controlled speed. Even then, we are not able to get Kiln feed LSF standard deviation under control. It is highly fluctuating. In this situation, how the kiln feed LSF can be brought under control?
Can you please explain the followingPoints?
How the bag filter dust LSF increases?
How lime enhancement takes place?
What is the material balance?
What is the chemistry involved in it?
Please explain.
Thank you and regards,
537 posts
Re: Kiln feed LSF
Hello GSMS,
How the bag filter dust LSF increases?
How lime enhancement takes place?
As Sheikh has pointed out above, the LSF of bag filter/conditioning tower dust will depend on the composition of the softest materials in your raw mix. For example, if the limestone component is softer than the argillaceous & siliceous components, then the dust will be richer in CaCO3 than the kiln feed, and consequently its LSF will be higher.
If the limestone component is a lot harder than the argillaceous & siliceous components, then the dust will be richer in SiO2 & Al2O3 than in CaCO3, and the dust will be lower in LSF than the kiln feed.
What is the material balance?
What is the chemistry involved in it?
Obviously, if nothing significant is lost from the system, input should balance output in both chemistry and quantity.
So, the total quantity of fresh, dry raw materials should equal the quantity of clinker, corrected for LOI and coal ash. This is also true for the chemistry.
However if we look at the quantity and chemistry of material streams within the 'black box' of the kiln system, it starts to become very complicated.
This is because every single material stream, from raw meal ex the mill to kiln feed entering the preheater tower usually has some sort of dust component to consider.
For example, most plants return their recirculating dust streams (bag filter,conditioning tower dust etc) to the kiln feed... either into the homogenising silo or to the kiln feed bin. This dust is then removed again in the top cyclones, so that the kiln feed leaving the top cyclones is close in chemistry to that of the fresh raw meal.
For example let's say a plant's fresh raw meal has an LSF of 99 and the raw mill average rate is 350t/h. If the total dust recirculation back into the kiln feed is 8% and has an LSF of 150, then the rate of dust recirculated (8/100*350 = 28t/h) and the LSF of the kiln feed will be (350 * 99 + 28 * 150)/(350+28) = 102.8
However, as soon as this kiln feed is fed into the top cyclones it loses this dust (which has an LSF of 150) at the rate of 28t/h, and its LSF returns to that of fresh raw meal (99).
Therefore the LSF of kiln feed depends on where you sample it and how you are handling the dust stream(s). A mass balance, such as I described above, simply quantifies the mass flow and chemistry of the material streams.
Hope this helps,
Ted.
20 posts